Isaac

Isaac is a Venus Adept, a playable character in Golden Sun and Golden Sun: The Lost Age, and a main character in the overall Golden Sun series. He is the silent protagonist and party leader of the original Golden Sun, and gains a speaking role in his appearance late in Golden Sun: The Lost Age as a co-leader of the game's extended final party. For being the most effective "main representative" of the Golden Sun series, Isaac serves a cameo role in the 2008 Nintendo fighting game, Super Smash Bros. Brawl.

=As a playable character=
 * Also see: Gallery of Isaac's GBA sprites.

Throughout all of Golden Sun, Isaac serves the most important gameplay role for the player in the game: he is the player. More specifically, he is the character who the player controls in the game's overworld and field-style environments and is the one who initiates conversations with Non-Player Characters and searches aspects of the environment. He is the "party leader" in Golden Sun, which means that as he leads a group of Adept companions through the game's plot and world progression, he is the only character among them who is actually visible as you control him and have him walk and run through the world's locales. Also signifying Isaac's role as party leader in the first game is his in-game depiction as a fully silent protagonist while his companions that appear in cutscenes engage in conversations for him. Isaac is not actually a muted character or a man-of-few-words in the actual story of the game; that is merely how he is depicted when under the control of the player for the whole game.

Another thing that comes with Isaac's role as party leader is his inherent knowledge of two particular Utility Psynergy spells: Move, the ability to remotely move an object in any one of the four compass directions, and Retreat, the ability to instantaneously teleport himself and everyone in his party out of almost any point in a dungeon-style location to that location's entrance point. The Venus Adept and party leader in Golden Sun: The Lost Age, Felix, begins the game inherently knowing these Psynergy spells as well.

In Golden Sun Isaac is present for every battle sequence that takes place. In fact, the game's prologue has the player controlling a younger Isaac that is weaker and has no Psynergy at all. The "normal" Isaac is controllable following the prologue sequences when starting off at the town Vale. Isaac is a warrior-style Venus Adept, which makes his inherent class series the Squire class series, and when the player first controls him he is level 1, has no Djinn, and is initially equipped with a Short Sword, Cotton Shirt, and Padded Gloves. Over the course of the game, Isaac should prove the best fighter of the party of Adepts he leads, being both stronger and faster than the Mars Adept warrior Garet he fights alongside with.

Isaac, like the rest of his party, is absent from your own party as led by Felix, Isaac's very similar Venus Adept counterpart, for much of Golden Sun: The Lost Age. At a late point in the game, Isaac's party joins Felix's as additional party members, and the statistics and inventory of Isaac as well as his companions Garet, Ivan, and Mia are directly dependent on whether you're using data transfer, what level of data transfer you're using, and the actions and levels of progress Isaac's party committed in the previous game.

If there is no data transfer used at all, Isaac will join at level 28, with five of the original game's 28 Djinn (instead of seven) Set onto him, and he will be equipped with a Great Sword, Knight's Shield, Knight Helm, and Steel Armor. Also in his inventory will be all the Utility Psynergy items the party is required to collect to reach the end of the first Golden Sun, without any of the items the party can potentially miss - namely, he'll have the Catch Beads, Carry Stone, Lifting Gem, Douse Drop, and Frost Jewel, and will be missing the Orb of Force, Cloak Ball, and Halt Gem.

Isaac easily has the exact same amount of potential as his Venus warrior counterpart Felix to be the best fighter in The Lost Age, and they share a trait that can make either of them far more powerful than the rest of the Adepts: The ability to equip the ultimate weapon, Sol Blade.

In Super Smash Bros. Brawl
Isaac is the only character from the Golden Sun series making a cameo appearance in another Nintendo video game, in this case the popular Wii fighting game Super Smash Bros. Brawl, which is his first 3D appearance in a console game. While Isaac is not a playable character, he serves a minor gameplay role by being one of dozens of minor computer-controlled Nintendo characters that can be randomly summoned during battle by the item called the Assist Trophy. Isaac will be unlocked as one of these randomly-appearing characters if you play over 200 Brawls in the Group mode.

If Isaac appears out of an Assist Trophy, he will cast the Move Psynergy three times in succession while yelling, each time calling up a giant gloved hand that shoots forward to push away any fighter that is an opponent of the fighter who summoned Isaac. He will automatically turn around to face the direction of valid targets in between his castings based on how many fighters are to his left or his right.

Consensus among Smash Bros. fans place Isaac as one of the strongest Assist Trophy characters in the game; the hands are rather tall and accelerate to a relatively good speed, causing any character that gets caught up in Move to likely be repeatedly knocked back in mid-air until they are "carried" off the stage, assuming there are no obstacles elsewhere. The "pushing" effect of Move is a demonstration of an effect in the game's internal mechanics called Set Knockback, which is knockback like it were coming from a character's attack but deals no damage and always sends the victim a certain distance back rather than a variable distance affected by the victim's life meter percentage. Isaac's Move Psynergy has the distinction of being the only thing in all of Super Smash Bros. Brawl that can knock back and potentially K.O. a character under the invincibility-granting effects of the Starman item.

Isaac's voice in all versions of Brawl is provided by female Japanese seiyu Aya Hara, who also voiced the Japanese Krystal in the same game (and Star Fox Assault). The three voice samples Isaac randomly projects during his casting the Move Psynergy include two battle yells and the word "Move".

Everything serving a gameplay role in Brawl is represented by collectible figurines called Trophies, of which hundreds exist, and each trophy showcases a 3D model of a character, object, or other property along with a short text description. Isaac is no exception, and his trophy is among the large proportion of trophies that can be collected by "normal means" in Brawl, such as in a trophy-collecting mini-game called the Coin Launcher. Its text description reads:

"A strong-willed Psynergy adept of the bloodline of an ancient race thought to have been lost with the downfall of civilization. He can manipulate earth-based forces and is also a highly skilled swordsman. He sets out to protect a lighthouse that can release the sealed powers of alchemy. In Smash Bros., he uses "Move" Psynergy, which creates an energy field that pushes foes away."

=Biography= Isaac was born in the secluded town of Vale at the base of the dormant volcano Mt. Aleph, and for his first fourteen years he lived a tranquil life there with his parents Kyle and Dora and his friends Garet, Jenna, and Felix. Like his parents, Isaac is a Venus Adept, and all the townspeople of Vale are Adepts to varying degrees because they live their lives under the influence of a giant Psynergy Stone formation near the town's entrance. Isaac was very reliable and was well-liked by the populace; as an individual, he is virtuous and caring yet not to a fault, and Dora describes him as being so much like his father at his age, including his stubbornness. Isaac used to visit the cottage of the scholar Kraden a lot as well before the elderly alchemist was kidnapped during Saturos' second raid on Sol Sanctum.

Having lived at Vale his entire life, at a mountainous area not close enough to the Great Western Sea, Isaac had never seen an ocean before prior to his quest in Golden Sun, like his friends at that point.

In Golden Sun
The story of the first Golden Sun is told through Isaac's perspective, so Isaac is the main character the player controls throughout the entire game, and becomes the silent protagonist the player may end up interpreting his or her own way.

The Mt. Aleph Boulder incident
The lives of Isaac and many others were changed forever when he was fourteen, when the Mt. Aleph Boulder incident happened at Vale: Mt. Aleph and Vale were beset upon by a terrible thunderstorm, and a giant boulder located somewhere on Mt. Aleph became dislodged and descended upon Vale, crashing through Jenna's house and pier - where Kyle, Felix, and Felix and Jenna's parents at the time were located. All four of of them seemed to disappear right before the eyes of Isaac, Garet, Jenna, and Dora. Lost and confused, Isaac wandered off on his own into the night and Garet followed him. The two boys were soon accosted by a duo of menacing strangers, Saturos and Menardi, who used their powerful Mars Psynergy to knock Isaac and Garet out cold so they would forget their memories of the duo, and the pair of Mars Adepts immediately left the area.

It goes without saying that the period of time following the disaster was very trying for Isaac and those he knew. Isaac and Dora were devastated by the apparent death of Kyle, but the trauma Jenna underwent eclipsed that, for she seemingly lost her entire family. Isaac felt that if he had been better at Psynergy, he could have saved his father; thus, he and Garet resolved to study the art of Psynergy hard over the next three years, with Kraden guiding their toils as a scholar of Alchemy himself, to become stronger both for themselves and for everyone else.

Infiltrating Sol Sanctum
In the present age, Isaac has become a strong, reliable young man who has developed his Psynergy powers as a Venus Adept, along with Garet and Jenna. One day, as part of their studies, Kraden arranges for an expedition for the three young Adepts and himself into Mt. Aleph's shrine, Sol Sanctum. Entirely by coincidence, however, Saturos and Menardi return to Vale that day, and they are overheard by Isaac and his friends audibly plotting on how to enter the Sol Sanctum themselves and remarking about Kraden, who they approached earlier. Then the two groups cross paths; following a brief but tense interaction, Saturos decides to let them pass (Isaac and Garet wouldn't remember the pair of Mars Adepts from three years ago since the memory was physically knocked out of them). The young Adepts immediately go to Kraden to speak about the strangers, and conclude they are likely here to rob the Sanctum, but Kraden states they cannot prove that until after they commence their own scheduled expedition, which they ensue immediately.

Kraden and Isaac's group secretly enter and explore Sol Sanctum, and eventually make it into the sealed chamber where the Elemental Stars await on their respective pedestals. Letting his curiosity overtake his better judgment, Kraden orders Isaac and Garet to remove and retrieve the Elemental Stars for him to study. Just as Isaac and Garet collect three of the four Stars, fate intervenes and Saturos and Menardi make an entrance, taking Jenna and Kraden hostage. They demand that Isaac and Garet hand over the Elemental Stars to them, and this time, the duo has other companions with them: A powerful Mercury Adept named Alex and, to everyone's disbelief, none other than Felix himself, who Saturos and Menardi had rescued from the disaster three years back and who now is sworn to their cause. Isaac and Garet submit to their demands and give them the three Stars, and go to retrieve the fourth Star for them.

When Isaac and Garet remove the last Star, the Mars Star, from its pedestal, the volcano that is Mt. Aleph begins to stir, and a boulder-like entity laced with immense power awakens and makes its presence known. When Kraden identifies the being as none other than the Wise One from the healer's tales at Vale, Saturos' group realizes it is too dangerous to remain in the chamber and are forced to make the personally troubling decision to flee while they can while leaving Isaac, Garet, and the Mars Star behind. Saturos needs all four Stars to carry out his group's plan, which is to activate the four Elemental Lighthouses situated across the world, which will cause the restoreation of the force of Alchemy to the world. They decide to take Jenna and Kraden with them as captives traveling as part of their group, in hopes that if Isaac and Garet escape on their own, they will immediately pursue Saturos in an attempt to free Jenna and Kraden from their grasp, which would would give Saturos the opportunity to retrieve the Mars Star from Isaac's possession.

Isaac and Garet, meanwhile, personally come face-to-eye with the monolithic Wise One, who declares to them that if the Elemental Lighthouses are lit, the world will be exposed to the threat of Alchemy. The Wise One explains that Alchemy can be a dangerous power if misused by the people of Weyard, so the lighthouses should remain unlit and Saturos' objective should be thwarted for the sake of the world's safety. The Wise One uses his powers to subtly imbue the Mars Star in Isaac's possession with an as-of-yet unknown property for an as-of-yet unknown purpose, then teleports Isaac and Garet to safety as the volcano erupts. As the Wise One redirects the flow of lava from the volcano away from the town, Isaac and Garet return to Vale safely.

Isaac and Garet attend as the main subjects of an urgent town meeting in Vale's Sanctum. After the Adepts explain everything to the worried townsfolk, the Great Healer receives telepathic messages from the Wise One, and declares that the fate of the world depends on whether Isaac and Garet will take up the quest to pursue and stop Saturos' group. He leaves the decision on this incredible responsibility to Isaac and Garet individually, but Garet is quick to leave his decision to Isaac, so Isaac must now decide for them both: Should Isaac refuse to accept the burden of the entire world as his own, he will not be able to take back his decision as he leaves the sanctum and the town. Thus would Weyard begin drifting towards its fated destruction.

In the canonical version of the game's story, Isaac does accept taking responsibility for the fate of the entire world, and the Wise One telepathically compliments Isaac and Garet for their bravery in taking up this quest. Isaac and Garet do not receive much in the way of instructions on how to start their quest off, however. Everyone decides for Isaac and Garet to spend one last night with their families at Vale, and then see them off as they start their journey the next day. Come the next day, Dora is too distraught to actually be there to see her son off on such a dangerous mission, so Isaac receives Dora's Catch Beads from Garet's brother Aaron in Dora's place. With everything said and done, Isaac's adventure across the world of Weyard in pursuit of his multiple goals hereby begins.

Mercury Lighthouse
Isaac and Garet initially don't have a specific location or direction in mind when they begin their hasty quest in pursuit of Saturos' party across the continent of Angara. Immediately, they start battling and killing off the many, many wild monsters roaming the lands that were driven feral by the influence of Psynergy Stones that Mt. Aleph's eruption scattered across the world, and the battling experience Isaac and Garet receive increases their proficiency at fighting and sharpens their Psynergy abilities somewhat dramatically. Isaac also meets and befriends a Venus Djinni, Flint, one of many small elementals that were also scattered across the world when Mt. Aleph erupted. Flint is the first of many elemental Djinn that Isaac and his group collect on their quest, and each one they find bolsters their combat and Psynergy abilities.

The first town Isaac and Garet come across is Vault, where they meet a mysterious young Jupiter Adept named Ivan. They help him retrieve an important artifact, the Shaman's Rod, that was stolen from him by the Vault gang of thieves. Ivan, using his Psynergy-based ability to read minds to learn everything that happened to Isaac and Garet and how it relates to the world's state of affairs, eventually decides to join Isaac on his quest and becomes a permanent part of Isaac's traveling group of Adepts from that point forward.

The course of Isaac's quest eventually leads his group to the wintry northern region of Angara, where they stop in Imil, the town near the Elemental Lighthouse of Mercury, which is likely Saturos' first target. They meet a female Mercury Adept and healer named Mia, who suddenly sees that the Mercury Lighthouse is generating reactions as if invaders entered it, so she and Isaac immediately go to the Lighthouse to investigate. After Isaac uses his Psynergy to remove some obstacles, Mia feels she can trust Isaac, and she joins Isaac's party as they climb their way up through the tower in search of who might be here.

At the aerie of Mercury Lighthouse, Isaac and Mia's party discovers to their great dismay that the Mercury Beacon has already been activated with the Mercury Star, a process which cannot be reversed by any known means. The culprits haven't left yet: Menardi and Felix and their captives Jenna and Kraden call out to them from the opposite end of the aerie, and Saturos himself soon steps out in front of the Adepts, complimenting Isaac and Garet's survival of the eruption of Mt. Aleph. Saturos stands ready to attack and defeat the four Adepts in battle as the others flee; he proves a very fearsome and powerful opponent indeed, but the Mercury-based power generated by the active Mercury Beacon is enough of a hindrance to Saturos' Mars-based abilities (consequently boosting Mia's Mercury-based powers) that Isaac's party manages to best him in battle.

Alex, who was watching the Adepts from afar, makes himself known at this point, complimenting Isaac on how he and his friends have become such great fighters in such a short amount of time. After confirming that Isaac still has the Mars Star with him, Alex helps Saturos up and leaves the Lighthouse with him via the elevator. Just as Saturos' group resumes their objective to activate the remaining three Lighthouses' beacons, Isaac's party resolves to resume their quest to stop Saturos from activating the other Lighthouses, but Mia decides to permanently accompany Isaac on his quest as well. Isaac's group is now fully rounded out with four members, one of each element.

Quest across two continents
Isaac leads his group of Adepts clockwise across the entirety of Angara in pursuit of Saturos' group of Adepts and unwilling captives, all the while entering new towns, taking part in subplots involving such individuals as the young woman Feizhi and the oracle Hama, and exploring and clearing dungeons and caves whose obstacles and wild monsters challenge Isaac's course. By the time the Adepts make it to the town of Kalay, Isaac and Garet have an opportunity to revisit Vale and temporarily reunite with their respective families, though by now Dora has grown ill with a cold out of worry over her son's safety. Knowing now that Saturos crossed the Karagol Sea southwest of Angara to the continent of Gondowan where the next lighthouse, Venus Lighthouse, awaits to be lit, Isaac's group takes a none-too-pleasant voyage on the ferry service across the sea, arriving at Gondowan and beginning the next leg of their quest.

The party of Adepts stop in Tolbi, the largest city in Weyard, which is currently in the midst of its world-famous annual festival and tournament of warriors, Colosso. But Tolbi's mysterious ruler, Lord Babi, is missing. The Adepts follow a lead into the nearby Altmiller Cave and soon discover Babi on the verge of death, and they save his life by bringing him the fluid Babi was seeking in the cave, Lemurian Draught which Babi had stockpiled within the cave a long time ago. Babi takes a keen interest in Isaac and his company's powers, and decides to personally register Isaac as a Colosso gladiator for the upcoming Colosso Finals so he may observe Isaac's abilities to their fullest extent. Isaac has no choice but to agree to participate, and he competes in the tournament exceedingly well.

Following the tournament, Babi is content to declare that he has finally found the warriors he was hoping to meet. As he explains, long ago he was at the hidden island city and society of Lemuria far out in the Great Eastern Sea, long believed by outsiders to be a myth because of how it is shrouded by perpetual fog and a ring of stone crags. Lemuria is a place where the power of Alchemy remains unbound, allowing its inhabitants to live far beyond their normal years. Using the Psynergy he learned there, Babi fled the isle on a Lemurian Ship with Lemuria's entire remaining stockpile of draught in tow. Babi is now 150 years old because he has been drinking this fluid to artificially extend his lifespan. But his draught stockpile has now run out, and he needs a group of Adepts like Isaac to commandeer his Lemurian Ship into the ocean and rediscover Lemuria so as to retrieve more draught for him. Babi hid his Lemurian Ship within the town Lalivero in the easternmost region of Gondowan, close to Venus Lighthouse, which coincidentally is Isaac's next destination. Babi also had ordered the construction of a lighthouse-like tower named Babi Lighthouse near Lalivero so that the powerful light it would illuminate at night would help orient sailors as they try to enter the foggy area of sea where Lemuria is hidden. With this in mind, Isaac promises Babi that once he has achieved his own objectives, he and his party will search for Lemuria and attempt to save Babi's life again. Babi assigns his chief minister, Iodem, to accompany Isaac as they travel to Lalivero and the Venus Lighthouse.

Venus Lighthouse
Isaac's party journeys to Lalivero with Iodem, but they learn from the distressed locals that Saturos' group passed through here with a young Laliveran girl named Sheba as yet another one of their captives. Iodem can only speculate what they would want with Sheba, but Isaac leaves Iodem behind with the Laliverans in Babi Lighthouse as he and his companions head through the Tunnel Ruins to Venus Lighthouse. By now they possess the power and Psynergy abilities necessary to solve the structure's ancient riddles and climb through the tower to its very top.

At the Venus Lighthouse Aerie, Isaac and his friends arrive just in time to watch as Saturos and Menardi, in front of the Lighthouse's unlit beacon, have a falling out with Felix over the involvement of Sheba, who is up there with them, in their quest. Isaac's group initiates a tense standoff with Saturos and Felix, but Saturos employs crafty wording to trick the Adepts into thinking that he would release Sheba if they trade to Felix the Shaman's Rod in Ivan's possession. The Adepts are exasperated when Saturos clarifies afterward that he only actually said he wouldn't harm her, and that he can't let her go: Sheba, after all, is actually a Jupiter Adept, and Saturos' group needs both her and the Shaman's Rod in order to properly climb through Jupiter Lighthouse in the future.

Saturos and Menardi then decide it is time for Isaac's party to die, and the duo launches an all-out offensive. Though the battle is fierce, Isaac's Adepts best the master Mars Adepts in the end. Isaac then tries to reason with Felix, but Felix insists that the Lighthouse beacons must still be lit even though he is not bound to follow Saturos anymore, forcing Isaac to conclude that Felix is their enemy. But Saturos and Menardi are not out of the picture yet: they casually toss the Venus Star into the Venus Lighthouse's well, to the horror of Isaac and his friends. As the Venus Lighthouse activates, the energy let loose recharges the duo. Saturos and Menardi then execute their ultimate power: they merge together to form a single, colossal, terrifying creature resembling a two-headed dragon. The dragon attempts to annihilate Isaac and his party of Adepts, but after an incredibly intense battle, Isaac ultimately slays the beast. The dragon reverts to the defeated forms of Saturos and Menardi, who fall backward into the Lighthouse's opening and meet their demise.

Isaac's incredible victory intimidates Felix into declaring that he is no match for Isaac now and that he must flee with Sheba to carry on Saturos' quest. Suddenly, the Venus Lighthouse wracks itself with a violent earthquake, and as part of the automated process that establishes the active Venus Beacon, the tower splits up into four evenly divided quarters. Sheba loses her footing and falls off the tower to certain death, and Felix, completely beside himself over what just happened, jumps clean off the tower after her, to the disbelief of Isaac and Garet. After the Lighthouse reforms itself and the chaos subsides, Isaac and his friends gather their thoughts: Saturos and Menardi are gone for good, but Felix and Sheba appear to have died too. They need to find Jenna and Kraden now, so they climb down and leave Venus Lighthouse.

In the period of time to come, Isaac and the Adepts conduct a long and tiring search for Jenna and Kraden around the vicinity, but they are never found. The people of Lalivero believe, however, that Sheba and Felix have actually survived their fall, because witnesses saw the base of the lighthouse get flooded by the ocean during the earthquake and the sea rising up to catch Sheba safely. The Adepts figure that Sheba and Felix must together with Jenna and Kraden and likely Alex as well, the latter three of whom were likely on the peninsula of land named Idejima that broke off the Gondowan mainland and floated out to sea during the earthquake. Iodem leads Isaac's party to Babi's Lemurian Ship, and entrusts Isaac the Black Orb that allows the Adepts to commandeer the Ship with their Psynergy. With their objectives laid out for them, Isaac, Garet, Ivan, and Mia resolve to sail across the oceans of Weyard in pursuit of their multiple goals: To stop Felix and Alex from unleashing Alchemy upon Weyard via the lighting of the Lighthouse beacons of Jupiter and Mars; to rescue Jenna, Sheba, and Kraden; and to uphold their promise to Babi to discover Lemuria and retrieve Lemurian draught in time to save Babi's limited life.

In Golden Sun: The Lost Age
In contrast to the previous Golden Sun, the story of Golden Sun: The Lost Age is told through Felix's perspective, so Isaac and his group are not encountered in person for much of the game. During his own quest Felix can learn what Isaac has been up to recently by talking with townsfolk at certain points in the game.

The Great Eastern Sea
For the next great period of time, Isaac and his party of Adepts sail their ship in an expedition across the Great Eastern Sea in search of Felix and their other objectives. Isaac is under his strong belief that the world would be in terrible danger should he fail his tasks, as per what the Wise One told him in Sol Sanctum. But until a chance encounter with Felix somewhere across the seas should occur, Isaac explores the sea and stops at various settlements in hopes of acquiring information important to his other, self-imposed objective of discovering Lemuria for Babi.

Isaac may or may not have made an attempt at this time to sail into the foggy, craggy Sea of Time where Lemuria lay hidden. Granting that Isaac does, even though the Venus Lighthouse is lit well enough that it substitutes for what would have been Babi Lighthouse's role of helping them keep their bearings in the treacherous sea, Isaac's group would have failed in finding Lemuria at first. This is because the initial ring of stone crags at the perimeter of the Sea of Time make for a complicated maze and obstacle course that cannot be navigated without special knowledge of how certain strong currents can be negated by sailing in specific patterns. And even if they had such knowledge, they would have inevitably been turned back by a monstrous demigod named Poseidon prowling the grounds, who is completely invulnerable to the forms of assault Isaac and his friends know.

After stopping to rest at the eastern island chain of Apojii Islands, where Isaac and company get to see Gaia Falls itself up close for the first time in their lives, Isaac sails southward to the continent of Indra. As he and his crew ask around in the town of Madra about Lemuria, Isaac comes to learn about a man who was held captive in Madra recently named Piers, who possesses a Lemurian ship just like Isaac does and has the ability to perform Mercury Psynergy. Isaac is shocked to learn of a man like Piers, who could very well be a Lemurian, and he declares he will follow Piers into the heart of lower Gondowan when he learns that's where Piers was last headed. Before leaving, Isaac is told the story of how Piers caused a puddle of water to magically turn into a pillar of ice, and he tells the Madrans how that was an example of a power called Psynergy, and he and his friends decide to show the Madrans some of their own Psynergy powers. For Isaac and Garet to do this is rather interesting because it is a law and code of Vale, their hometown, not to show Psynergy to outsiders.

Isaac is very determined to meet with Piers, believing the Lemurian to be his last chance to enter Lemuria and fulfill his promise to Babi. He and his friends stop in the southernmost town on Gondowan, Naribwe, and Isaac pays the innkeepers a large sum of coins for them to pass the message onto Piers the next time they see him that Isaac wants to meet him. Then Isaac's party apparently travels northward to Kibombo only to be ultimately turned back by the Kibombo warriors stationed at the Kibombo Mountains (who have increased their numbers and security after Piers went through there earlier). Isaac and his group are never able to meet Piers throughout the Great Eastern Sea. Thus the inevitable news comes: Babi has finally died in Tolbi. It would be understandable to assume that this failure to save someone's life would weigh heavily on Isaac and his perspective on his own quest, since Isaac was unable to keep his promise despite his best efforts.

Jupiter Lighthouse
Isaac and his companions sail through the divide between the continents Gondowan and Indra to make it into the Great Western Sea, and they moor their ship at the island continent of Atteka, which is where the next lighthouse they must protect from Felix, Jupiter Lighthouse, is situated. After they pass through the town of Contigo along the way, they rush into Jupiter Lighthouse.

During their exploration of Jupiter Lighthouse, however, the Adepts are divided by a trap that separates Garet and Mia from Isaac and Ivan. Shortly afterward, a pair of Mars Adepts, Karst and Agatio, present themselves as the ones responsible for the trap. Isaac correctly judges from their appearances that they are closely related to Saturos and Menardi; Karst is indeed the younger sister of Menardi, and she and Agatio have come from their hometown of Prox far up north to destroy Isaac in revenge for Isaac's murder of Menardi. Isaac, strained from his quest and prior events as is, tries to brusquely tell Karst and Agatio off and say he'll save his friends on his own, but the pair launch their assaults toward Isaac and Ivan with the intent to kill.

Isaac and Ivan are eventually overpowered and defeated by Karst and Agatio in a desperate battle, and the Mars Adepts are about to finish them off when Felix and his party of Jenna, Sheba, Piers, and Kraden step in to stop them. Karst and Agatio interacted and dealt with Felix's group of Adepts previously, but Felix declares his intent to keep Isaac from further harm, and he and his party force Karst and Agatio into a deal where Isaac's life is spared if Felix takes the Mars Star Isaac has in his possession, and then activates the Jupiter Lighthouse with the Jupiter Star Felix has. As Isaac lies on the ground, he sees that Felix was willing to save him from death despite their being at odds for their entire quest, and though Isaac does not know why Felix is so set in releasing Alchemy, he places his trust in his former childhood friend and gives up his Mars Star to Felix. Felix and Piers then follow Karst and Agatio up to the top of Jupiter Lighthouse as the other three are left behind to tend to Isaac and his party.

With Garet and Mia saved from the trap and Isaac and Ivan patched up, Jenna and Sheba suspect something might be wrong and they check up on Felix. Once Isaac's party fully recuperates, they head up to the aerie of Jupiter Lighthouse where they find Felix's party has just conducted an intense battle with Karst and Agatio, who have now escaped (with the Mars Star now in their possession, as they have taken it from Felix). Isaac demands an explanation from Felix about everything, but everyone is quick to agree that this isn't the best place to discuss all the circumstances, and Felix promises Isaac that they will meet officially in Contigo. Isaac leaves them and Jupiter Lighthouse on this note, sternly warning that Felix can not just sneak off again.

The Reunion
Isaac, Garet, Ivan, and Mia stake out in an empty house in Contigo and wait until Felix and his party of Jenna, Sheba, Piers, and Kraden arrive to begin their meeting. In the epic interaction to follow, it is first explained that Felix was always trying to avoid Isaac because he couldn't face Isaac after he assisted Saturos and Menardi in raiding Sol Sanctum and thereby betraying their hometown of Vale, and also that if they had met prior to this point they would have ended up fighting each other, which Jenna in particular could never want. As to why Felix helped Saturos, Isaac is shocked by the truth to say the least: Felix and Jenna's parents, as well as Isaac's father Kyle, were not killed in the Mt.Aleph boulder disaster three years back. Saturos and Menardi - the ones who had originally triggered the disaster - had rescued the parents from death just as they had saved Felix, and the duo brought them all back to their hometown of Prox. For the past three years the parents lived in Prox, nominally incarcerated at the town by Prox's people on Saturos' suggestion. The parents were to be kept captive at Prox until Saturos's quest to restore Alchemy to the world would be complete; Felix had thus been coerced to join Saturos in his objective, motivated by the prospect of winning his parents' freedom.

Isaac then learns something even more incredible from Felix's side, something that Felix's party discovered during their own quest: Alchemy's absence from the world of Weyard over the past many ages has let the world descend into a gradually deteriorating, dying state in a very physical sense, with the continents of the world gradually breaking up and sinking into the oceans, and with Gaia Falls consuming more of the world's perimeter. The world effectively has a life force that is literally sustained by the presence of the force of Alchemy, and if Alchemy is not brought back in time, Weyard will collapse into an eventual yet inevitable doom. This revelation makes the current circumstances all the more concerning for Isaac, as he and everyone else believe there could be a risk of Alchemy destroying the world if its seal is broken, but if they don't take that risk the world will definitely end.

Finally understanding why Felix and those he allied with were trying to activate the Elemental Lighthouses, Isaac makes the decision to join forces with Felix's party, proclaiming that this is Felix's quest which he is now helping out with. Then Hama, the oracle who Isaac met earlier in his own quest, comes in to announce that Felix's Lemurian ship now has a pair of magic wings attached to it, allowing the ship to fly. She also brings notice that with three of the Lighthouses now active, the element of the last unlit Lighthouse, Mars, is being suppressed on a global scale, causing the world to gradually get colder, and the world will freeze if Mars is not activated in time. And though Karst and Agatio are headed up north to try to activate the Mars Lighthouse for themselves, Hama senses that they will fail because there is a powerful force of some kind that does not want to see Mars rekindled. Isaac's crew joins Felix as they set out together on the latter's flying ship north to Mars Lighthouse to take the Mars Star back and activate Mars themselves.

Mars Lighthouse
Felix and Isaac lead their combined group of Adepts north into the bleak, blustery landscape of the Northern Reaches, and make it to Prox. The hometown of Saturos, Menardi, Karst, and Agatio, Prox is located near the Mars Lighthouse, itself located very close to the edge of the world. Isaac learns from the people of Prox, their Elder, and their chieftain Puelle the history and motivations behind Saturos and Menardi: The edge of the world is steadily consuming the landscape south in the direction of Prox, and Prox knew from the beginning that this was caused by the seal placed on Alchemy. So, they had originally sent out their strongest warriors, Saturos and Menardi, on a mission to retrieve the Elemental Stars from Sol Sanctum and break Alchemy's seal before the town, and eventually the entire world, would be doomed.

When it is brought to Prox's knowledge that it was Isaac who killed Saturos and Menardi, Isaac jumps and assumes combat stance, but Kraden quickly tells him off and clarifies why things had turned out the way they did; Isaac cannot be blamed for pursuing the pair to regain the Elemental Stars they stole after the pair triggered a volcano that endangered Vale. Prox comes to pardon him on the basis that Isaac should be prideful that he is stronger than they were, and that now he and the others are slated to see Saturos' original objective through to its end. Karst and Agatio went to Mars Lighthouse earlier, but have not since been heard from, so it is decided they should search for them too.

Puelle had given the order that Kyle and the parents of Jenna and Felix are to be set free once Felix returns to Prox. Isaac and Felix's group rushes to where the parents were supposed to be kept safe in a house, only to find that their parents are nowhere to be found in Prox. Evidence indicates that the parents went up towards Mars Lighthouse for some reason. Unsure of what could be happening, Isaac and Felix ready themselves and begin the final leg of their journey into Mars Lighthouse.

As the band of Adepts explore and battle their way through Mars Lighthouse, they encounter, battle, and dispatch a pair of lumbering, powerful Flame Dragons. The defeated dragons suddenly transform back into the defeated forms of none other than Karst and Agatio. The Mars Adepts, near death, relate their story of how they were stopped in their tracks and were gauged by "the eye" to lack the will and conviction to go any farther, and were turned into mindless dragons that were sealed in captivity. Because Karst and Agatio shared Saturos and Menardi's ultimate objective to activate all four Elemental Lighthouses, they entrust the Mars Star to their former "enemies" Isaac and Felix so that Isaac can complete the quest for everyone. Isaac and Felix then lead their group to the aerie of Mars Lighthouse.

At the Mars Lighthouse Aerie, Isaac and Felix's party are confronted by none other than the Wise One himself. The Wise One demands to know why Isaac has disobeyed his command to recover the Elemental Stars and is trying to break Alchemy's seal, and Isaac and everyone else respond with everything they now know about how the world would be destroyed if Alchemy remains sealed. The Wise One counters with the scenario that mankind may very well destroy Weyard themselves if allowed use of such power, and he states that in time, one man will seek to rule over all, which is an inescapable facet of human nature. The Wise One then reveals that the Adepts have all been played for fools from the start: Alex has used them all, and is currently climbing Mt. Aleph awaiting the lighting of the Mars Beacon so that when Alchemy is returned to the world, he will be at the center of the process and gain supreme power for himself. Everyone is thunderstruck, but Isaac loses none of his resolve in declaring that the beacon must be lit regardless, for the sake of the entire world's survival.

The Wise One declares that the Adepts will only be able to light the Mars Beacon if they can "defeat a miracle", then summons a colossal dragon with three heads for them to battle. As the Adepts steel themselves for their final battle, Isaac manages to see the Doom Dragon for what it really is: An amalgamation of the very parents they were trying to find before, including his father Kyle, forced by the Wise One to fight the Adepts without the Adepts being aware of who they would be killing until it would be too late. Isaac, in his greatest demonstration of his virtue, is willing to sacrifice what he holds most dear to his heart for the sake of the world, and helps his allies slay the dragon in an epic clash. Following the battle, even as everyone else is horrified when they first discover who they had really killed, Isaac remains strong and stoic; he declares that what they have done was to defy the Wise One in order to save the entire world, which is something Kyle and the other parents would understand. Everyone else finds it within themselves to agree with Isaac. With the quest almost at its conclusion, Isaac remains with his father as Felix casts the Mars Star into the Mars Lighthouse's well.

Epilogue
With the Mars Beacon lit, the process that will give shape to the Stone of Sages at Mt. Aleph and herald the return of Alchemy to all of Weyard begins in earnest. Like the other Lighthouses, the Mars Lighthouse generates an immense amount of raw elemental power as its beacon shoots a light into the direction of Vale, and all of the Adepts present at the aerie of Mars Lighthouse absorb a great deal of energy into their bodies. This includes the bodies of the fallen parents, and in nothing less than a miracle the parents are revived by the energy. Isaac and Felix and their party of Adepts transport their parents and themselves down out of the Lighthouse and across the landscape back towards Prox, and the people of Prox nurse the parents back to health.

Isaac, Felix, and Kraden are personally thanked by the Elder of Prox and Puelle for saving their town and the entire world, and for effectively bringing about a new, golden age where civilization may once again advance. They discuss what might have happened to Vale physically because of all the energy that was released above the town at Mt. Aleph; Isaac is most concerned about his mother's health, since the last time he saw her she was ill in bed worried for her son's safety. As everyone boards the ship due back home to Vale, Isaac also asks Kraden and Felix why everything happened at Mars Lighthouse the way they did: The Wise One had turned the parents into a dragon that Isaac and the others were forced to fight and pretty much kill, yet the way the parents were revived back by the beacon's light suggests the Wise One had to have known that would happen in advance. Kraden hazards a guess with wild implications: The Wise One's actions were all part of his grand scheme to test Isaac and his companions as individuals capable of the great responsibility of ensuring that throughout the world, Alchemy is not abused and used for evil.

Finally, Isaac and the Adepts, the three parents, and Kraden return to Vale, but are emotionally impacted by a tragic sight: Mt.Aleph and Vale are effectively gone, having been erased by the energy let loose by Alchemy's release. Isaac and Garet believe that Dora and all of Garet's family have perished along with all of the townspeople of Vale. But then, Dora and everyone else believed to have perished appear alive and well and greet the Adepts, revealing that the Wise One warned them to evacuate Vale before the town would be destroyed by the breaking of Alchemy's seal. Isaac and Kyle embrace Dora together for the first time in three years, and The Lost Age ends as everyone celebrates.

The epilogue of The Lost Age shows that when Alex stood in the beam of pure Alchemy shot down into Mt. Aleph by the sphere of energy formed by the merging of the energy beams of the four Lighthouse Beacons (the Golden Sun), he did gain bolstered power and life, but not the full mastery of reality Alchemy should have provided him. It is revealed that this was a precaution the Wise One took a long time back in Sol Sanctum: Recognizing the circumstances in the present and future when he awoke, he imbued Isaac's Mars Star with an effect that would cause the Mars Beacon's power, and thus the Mars portion of the Golden Sun, to enter Isaac's body at Mars Lighthouse rather than Alex's at Mt. Aleph. Isaac is now the unwitting bearer of the portion of the power of the Golden Sun that Alex now lacks. Alex in the meantime appears to have disappeared along with the mountain as it sunk into the ground.

=In Golden Sun DS= Currently known plot-wise about Golden Sun DS from this E3 press release is that the main characters are descendants of the previous games' heroes, and an issue of Nintendo Power magazine claims that the main playable character is the son of Isaac. This purported son is most likely the pictured character, as seen in this promotional art, but fan circles are only able to speculate on related details until further information is released.

=Trivia=
 * Isaac is the only character in the Golden Sun series to have made an appearance in another game outside the series, namely as a supportive cameo role in Super Smash Bros. Brawl, and this appearance is his first 3D appearance in a console game and the first time his voice, or the voice of any Golden Sun character for that matter, is heard.
 * Isaac's trademark scarf appears to switch which shoulder it rests on depending on whenever he is depicted as battling or not battling. In his official artwork, portraits, and images pictured above, his scarf is draped over his left shoulder, while his in-game battle sprites and, more recently, his Super Smash Bros. Brawl appearance as a fighting Assist Trophy depict his scarf over his right shoulder. This may be an intentional visual quirk or a meaningless coincidence.
 * Along with his scarf, Isaac's sword also seems to switch shoulders, where, in his official artworks and trophy in Super Smash Bros. Brawl, it is over his left shoulder, while his town map and frontal sprites have it over his right. Thus said, although Isaac's battle sprite shows that he is obviously right-handed, it's debatable whether he truly is or not.  This could be, like his scarf, a meaningless coincidence or a simple spriting mistake.
 * Following the Reunion, where Isaac's party joins Felix on Felix's ship late in The Lost Age, Isaac's own ship has apparently vanished. A commonly presented answer as to why it's never seen in the game, outside of accusing the developers of negligence, is that Alex may have stolen it for himself at this point, and used it following the events at Jupiter Lighthouse to sail back to Angara and begin his final journey towards Mt. Aleph.
 * The August 2009 issue of the U.K.-circulated Official Nintendo Magazine made the erroneous claim that the main playable character seen in the E3 trailer for Golden Sun DS was Isaac himself, rather than a descendant of Isaac as confirmed by the E3 press release. Nintendo Power reported him to be Isaac's son beforehand; however, due to Nintendo Power magazine being separated from Nintendo themselves, this claim is still pending.

Sidequest roles

 * Isaac is the main subject of the main optional events that happen in Golden Sun: The Lost Age based on what Isaac and his party achieved in the original Golden Sun and whether that game's completed save data is used for data transfer:
 * Early in Isaac's quest after the eruption of Mt.Aleph, he and Garet join Ivan in taking down the Vault gang of thieves and locking them up in Vault's prison for the crime of larceny during a time of disaster. If Isaac and the other Adepts return to Vault later in the game and speak with the town's mayor, they will learn the thieves broke out of their prison somehow and seek vengeance upon him. Early in Felix's quest in The Lost Age, after Felix meets Karst (seeking vengenace on Isaac herself for his killing her sister Menardi, no less) for the first time in Madra, he will be stopped in his tracks by the bandits as he leaves the town, and they will take out their frustrations about Isaac by attacking Felix's group, but they easily lose. The thieves, threatened by the prospect they might go to jail again, apologize and run away, leaving behind the Golden Boots for Felix to use and equip.
 * During the portion of Isaac's quest that takes place in the Xian region of Angara, a subplot involving the young woman Feizhi and her friend Hsu will play out, with Hsu being trapped in Alpine Crossing by a landslide. Isaac, after having Ivan learn Reveal and before entering the Lamakan Desert, may decide to backtrack to Alpine Crossing and free the injured Hsu from the trapping boulder using the Lift Psynergy. Feizhi is thankful enough to Isaac that after the latter leaves to resume his quest, Feizhi develops a romantic crush on him and decides to make a good-luck charm called the Golden Ring which she'll give to him the next time she sees him. During the Great Eastern Sea portion of The Lost Age, Felix's party would be stopped by Feizhi the first time they enter Champa, and Feizhi mistakes Felix for Isaac because she predicted the Venus Adept coming into Champa and assumed it was Isaac. Feizhi entrusts the Golden Ring to Felix so that Felix may give it to Isaac later (which is an event not explicity depicted in the actual game).
 * During Golden Sun, if Isaac actually wins the this year's Colosso tournament, he will gain a moderate degree of fame as a gladiator and make some vengeful rivals among his fellow Colosso warriors who suspect his victory came from his matches being rigged, rather than some sort of spiritual force named "Psynergy". Several of the Colosso competitors will appear across the Eastern Sea, with some asking Felix to warn Isaac that several other Colosso Gladiators are seeking revenge. As such, late in The Lost Age when Isaac's party has joined Felix, the three Colosso Gladiators Isaac beat previously will ambush the party in Shaman Village Cave and demand a rematch, but are easily defeated again by the powerful party of Adepts. The gladiators will apologize to Isaac for their actions and receive Isaac's forgiveness, and they give him the Golden Shirt they found earlier in the cave, and as they leave they suggest maybe they can compete against Isaac again in the next Colosso.
 * Late in Isaac's quest through upper Gondowan, he will have the opportunity to discover and explore the legendary island cave in the Karagol Sea, Crossbone Isle, and he and his party are powerful and capable enough as Adepts by that point to solve all the island's tricks and traps, loot all its treasures, and possibly even defeat the terrifyingly powerful ancient ghost pirate protecting the treasure, Deadbeard. Once Isaac's deeds are done, pirates across Weyard will somehow learn of it and Isaac's identity, and recalling the stories that the one who defeats Deadbeard will gain the honorific of leader of all pirates, buccaneers will start seeking out this apparently tough and reliable man to join his pirate crew. If the game file where Deadbeard is defeated is used for data transfer into The Lost Age, then in the town of Alhafra, after the pirate Briggs flees the town on a ship and departs back for Champa, a pair of swashbucklers will appear in the second floor of Alhafra's inn as the town updates. The moment Felix's party comes in, an optional cutscene will occur where the two talk about Isaac's exploits and state that that means Isaac is their leader now, and that is why they are now looking for him so that they can join his crew. Then they will pass by Felix's group as they leave the inn on their search. It should be noted that this cutscene can occur anytime after when it can first occur, meaning that it can be triggered late in the game when Isaac's party has joined Felix's. In that case, though, the cutscene will play out exactly as it would otherwise, and the pirate pair will not realize they just passed by their new "leader" as they leave the inn in search of him.

=Quotes=


 * In McCoy's Palace
 * Game message: (in Lady McCoy's room) "Isaac peeked into the wardrobe... There's a silk negligee. Isaac! Put that back!"


 * At Venus Lighthouse:
 * Isaac:"!!!"


 * At Jupiter Lighthouse:
 * Isaac: (To Karst and Agatio, while Garet is in peril nearby) "If you're not here to help my friend, then get out of my way, so I can do it myself!"


 * Isaac: "Go on, Felix. Take it. I don’t know why you’re doing this, but I trust you… Take the Mars Star."


 * Isaac: "F, Felix... No! Why are you helping them?"


 * Isaac: (If Felix loses his battle with Karst and Agatio, and after Karst and Agatio leave) "Blast! They must have taken the elevator to escape!"


 * Jenna: "We'll be there, Isaac. I hope you still trust me."
 * Isaac: "I’ve never stopped trusting you, Jenna. I'll be waiting for you in Contigo." (To Felix) "We'll be expecting you. Don't think you can sneak out of this! You owe us an explanation!"


 * During the Reunion at Contigo:
 * Isaac: "Wait for the end of the world to come or wind up accidentally triggering it ourselves… What a choice…"


 * Isaac: (To Felix) "Why did you wait so long to tell me? I would have helped you..."
 * Kraden: "You wouldn't have done it before, Isaac... It would have meant violating the sacred teachings of Vale."


 * Isaac: "Listen, this is Felix's quest now… We're just doing what we can to help out..."


 * At Mars Lighthouse:
 * The Wise One: “The people of Prox have committed an unforgivable sin. They must pay the price.”
 * Isaac: “For lighting the lighthouses? Is that their sin? Does that warrant total destruction?”


 * Isaac: (After learning of Alex’s deceit) "None of that matters now. We still have to light the beacon. We don't have any choice. If we don't do it now, Prox will be destroyed! Felix… We have to, right?"


 * Isaac: (After killing the Doom Dragon, which was revealed to actually be Isaac's father and Jenna's parents that the Wise One forced the Adepts to fight and slay) "That's enough… I knew what I was doing the moment I raised my sword. We defied the Wise One in order to save the world. Our parents would understand."


 * Isaac: "Our quest is almost over. I...don't know how I'm going to tell Mom about this... But sorrow can wait. We've got to light the beacon."


 * Epilogue at Prox:
 * Isaac: "We're just glad to have helped save Weyard..."


 * Kraden: "Well, I suppose we should be departing for Vale soon."
 * Isaac: "You're right, Kraden... If we don't, might start causing trouble..."


 * Isaac: "I just want to be home again... I want to see how my mother is doing..."
 * Kyle: "Don't worry, Son. I'm sure Dora's doing fine. She's a strong woman."
 * Isaac: "But last time I saw her, she looked so sick, so weak... Even if nothing happened to Vale, I'm still worried..."
 * Kyle: "Don't worry, Isaac. I'm sure she's in wonderful shape. I think she'll be surprised to see me!"


 * Isaac: "It looks like we've got an exciting last trip ahead of us, doesn't it?" (If Felix says yes) "Wow... Setting out like this takes me back to our own quest's start... It was so long ago."


 * Isaac: "If [Vale]'s not there, then what's the point in even going back?"
 * Kraden: "Is that really how you feel, Isaac?"


 * Isaac: "Kraden... Why did the Wise One change our parents into a dragon? Why did he make us fight them? I mean, we almost killed them... He tried to make us kill our own parents. Why?"
 * Kraden: "Do you think that he intended for them to die from the start?" (If Felix says no) "Ah... You don't understand why he put you through all this if he knew they'd survive... We cannot hope to fathom the motives of a being as all-powerful as the Wise One..."
 * Isaac: "You don't know either, Kraden?"
 * Kraden: "I can only hazard a guess... The Wise One... wanted to test you."
 * Isaac: "What do you mean, test us?"
 * Kraden: "I cannot tell you more... It is up to you to find the answer. Will we use Alchemy to wage war, to raise armies? Or will we use it to grow wise, to rise above our petty feuds and perform great deeds? You were willing to sacrifice everything for this quest. I'd say you've risen to this challenge."


 * In the Battle Mode lobby:
 * Isaac: (If you lost a battle and Isaac was not in your party at the time) "You win some, you lose some. That's the nature of competition.

=In fan circles= Isaac is obviously one of the main characters and points of interest in the Golden Sun fan fiction community, Isaac's shippings are fiercely debated. The two main shipping is the Mudshipping scenario that romantically involves him with Mia. The other is Valeshipping which depicts him with Jenna, and both are from Vale. Although it is still small there seems to be a growing movement pairing Isaac with Ivan.

Portions of the fanbase disagree with the personality Isaac was given for his speaking role in The Lost Age because he seems curt and abrasive from when he first appears at Jupiter Lighthouse, and his nature as a silent protagonist in the first Golden Sun prompts players to come up with their own interpretation of Isaac (as is the essential purpose of being a silent protagonist), which likely wouldn't match how Isaac actually is in the second game. It should be noted that Isaac's attitude in The Lost Age would be consistent with what has been going on in his side of the story prior to this appearance, however, for in his side he had tried his hardest to enter Lemuria and save Babi's life like he originally promised Babi in Golden Sun, but eventually failed.

Isaac has been featured as a contestant character in the annual GameFAQs Character Battle series of popularity polls since 2007. He was unable to make it past the first round in late 2007 as well as late 2008, but was able to beat Professor Layton to advance to the second round of early 2010, where he was pitted against and had lost against the "joke character" L-Block (representing the Tetris series and which had won as the grand prize winner of the 2007 battle). (As a minor detail, just before the poll was posted, the user-submitted image representing the poll had the unnamed protagonist of Golden Sun DS erroneously pictured as "Isaac" as seen here, but was fixed in time.)

Isaac