Karst

Karst is a Mars Adept who, along with her partner Agatio, serves as one of Felix's primary antagonists in. As a duo of powerful and driven warriors who depart their home village of Prox to ascertain the safety of the previous game's antagonists, Saturos and Menardi, Karst and Agatio follow in their footsteps both literally and in spirit. Though Karst is dedicated to Saturos' original duty to break Alchemy's seal by reigniting the Elemental Lighthouses, she pressures Felix into lighting the remaining Lighthouses when she discovers that Menardi, her elder sister, died in battle against Felix's rival from the first game, Isaac. Karst swears to take revenge and kill Isaac to avenge her sister.

Biography
Karst hails from Weyard's northernmost settlement, the town of Prox, located near the edge of the world far in the Northern Reaches. She and the other denizens of Prox have a strong affinity to the Mars element because they are the descendants of the ancient Mars Clan based around nearby Mars Lighthouse, which may play into the somewhat draconian aspects of their appearances. Karst's face only features one natural facial marking under her left eye, whereas Menardi had such markings under both eyes; this may be tied to Karst's comparatively younger age. While Karst seems to be among Prox's most powerful warriors regardless, Agatio appears to have a higher position of authority in Prox's military hierarchy, second only to Saturos in power and therefore in rank.

Just before the events of Golden Sun, Karst and Agatio stay behind in Prox as Saturos and Menardi depart on their assigned quest to steal the Elemental Stars from Sol Sanctum and use them to light each Lighthouse's Elemental Beacons, thus releasing Alchemy and saving Prox from the encroaching abyss that is Gaia Falls. Karst is at least somewhat aware that one of the individuals departing with Saturos is Felix, whom Prox has coerced into cooperating with Saturos' quest by keeping his parents captive in the village. It is unknown whether she is aware at this time of a fourth Adept accompanying the group on their quest, Alex.

Trapped in the Eastern Sea
Through unclear circumstances, Karst ends up sailing out of Prox with Agatio, both intending to search for Menardi across the world's vast expanse to ensure her well-being. This apparently takes place either right around the time Venus Lighthouse is lit by Menardi and Saturos' efforts at the climax of Golden Sun or some time before then, since Karst and Agatio have already made it into the world's Eastern Sea when the tidal wave indirectly set off by the Venus Beacon washes over much of the southwestern Eastern Sea. This wedges the island continent of Indra between Gondowan and Osenia, which blocks off their way back into the Western Sea where Jupiter Lighthouse and the way back to Prox are located. Karst and Agatio presumably spend a while canvassing the eastern part of the world's surface in search for Menardi. Eventually, the Mars Adepts beach their ship on Indra and split up, with Agatio heading up north into southern Gondowan to check a village there.

Karst is seen standing idly in the village of Madra, calling out her sister's name without much apparent purpose or direction, when Felix returns to Madra from a trip up north into Gondowan. She does not even recognize Felix until she hears someone else call him by that name, and she demands to know where Menardi is. She seems to shrug off Sheba's rather pointed lack of tact when the latter says up front that Isaac had killed Menardi and Saturos, but the awful truth dawns on Karst when she observes that Menardi would never have left Felix to travel on his own. Despite Kraden's effort to head off Karst's building vengeance toward Isaac by posing that Felix hypothetically could have defeated Menardi, Karst dismisses that idea by logically observing that Felix would never have had the power to come close. Besides, as Karst sees it, Felix would never endanger the lives of his own parents back at Prox by betraying the Mars Adepts.

Karst "congratulates" Felix for having successfully lit Mercury Lighthouse and Venus Lighthouse but also reveals to him that the only real reason that happened was because Saturos and Menardi had researched how to climb each of the four Lighthouses prior to setting out on their quest. Saturos and Menardi had never told Felix about that, and now Karst expects Felix to open the way back into the Western Sea and light Jupiter Lighthouse on his own. Karst all but coerces Felix into agreeing to let her and her partner find and "take care of" Isaac, and she storms off swearing that she will make Isaac pay with his life.

Before Karst and Agatio take their boat back out to sea, Alex suddenly approaches them and offers to accompany them, and the Mars Adepts learn important details such as Isaac's party being the current bearers of the Mars Star. Though he had broken away from Felix's party after Menardi's death, he now believes Felix is more useful than Karst would give him credit for, so he directs her and Agatio to wait with him at Champa until Felix's party arrives. Alex lets Karst and Agatio threateningly pressure Felix's side into keeping his party focused on opening the way to the remaining Lighthouses. However, Alex conveys to the duo that Felix is ultimately the best-equipped among them to light Jupiter because he had previously retrieved a stolen item from a warlike tribe without recklessly terrorizing the tribe with his Psynergy, something Karst and Agatio would have failed at.

Alex goes further and reveals to the duo that the deceased Saturos and Menardi miserably struggled in their efforts to solve the riddles of the first two Lighthouses, and he does not dress up his language when he calls Karst and Agatio similarly "simple brutes, incapable of logic and intelligence." Karst is stunned enough to ask whose side he is even on, and Alex makes his stance clear that he is not on anyone's "side." As he is simply concerned with the lighting of the Lighthouses, he had wanted to introduce the Mars Adepts to Felix to "scare" his party into hurrying up with his quest rather than have the duo take the Jupiter Star from him and light Jupiter themselves. Karst and Agatio put up with having been "used" in this anticlimactic manner and leave Felix be, and Karst departs with the foreboding parting words that they will always be nearby to push him toward Jupiter Lighthouse.

Though Karst, Agatio, and Alex presumably stay close to Felix during the latter's voyages across the Eastern Sea, they apparently never feel any need to step in and criticize Felix for taking too long, even though Felix ends up exploring various ancient ruins to expand his group's powers and enter the hidden island society of Lemuria. Right after Felix leaves Lemuria, he uses a powerful form of Venus Psynergy to open the blocked-off naval route between oceans and enters the Western Sea.

Revenge effort at Jupiter Lighthouse
By the time Felix's party has begun climbing Jupiter Lighthouse on the continent of Atteka, Karst, Agatio, and Alex have landed on Atteka, and they follow him inside. In turn, Karst's side becomes aware that Isaac's party has also entered the Lighthouse, seeking to stop Felix from using the Jupiter Star to light the Jupiter Beacon. Knowing and being appropriately wary that a Mercury Adept named Mia is part of Isaac's number, Karst and Agatio set up a trap using a mechanism at an outdoor balcony, and they set it off just as the party walks over a retractable bridge to cause Mia to plummet onto another ledge below. This effort to divide Mia from the rest also snags Garet, much to the Mars Adepts' delight, and Isaac and his companion Ivan are left unable to do anything.

Karst and Agatio soon step forward to take responsibility for the trap and inform Isaac that he has a "little debt to repay." They relate their obsessive outlook that Prox stands to "recover its lost power" and make all of Weyard "kneel" before it, and Karst rubs it in Isaac and Ivan's face that they aren't even interested in a "fair fight," since they had also allied with Alex. It takes Karst a moment to realize that Alex never stepped out with them and has, in fact, abandoned them, but she and Agatio remark that they'll just deal with him later and confidently engage Ivan and Isaac in a two-on-two fight regardless. For the Mars Adepts, this battle is surprisingly fierce and closely matched, but the duo eventually beat the young Adepts down to the ground as a result of Isaac unavoidably getting distracted by Ivan falling in battle first.

Just as Karst and Agatio are on the verge of killing Isaac, she is surprised when Felix's party arrives at the scene and finds it to be a depressingly "typical" betrayal when Felix tells her that they are not leaving Isaac behind. Karst wastes no time recognizing that she has little choice in the matter; both she and Agatio will be destroyed if they fight all of Felix's party now, and Karst is not inclined to let her admitted rage against Isaac blind her to this. Therefore, Karst has Felix swear an oath to take the Mars Star from Isaac and light Jupiter Lighthouse, and the duo head up to the aerie and wait until Felix arrives with his companion Piers. Felix casts the Jupiter Star down the well, and the Jupiter Beacon is lit.

Karst and Agatio then break it to Felix that they don't need to continue brooking his traitorous streak because Mars Lighthouse is in Prox, which means the duo believe they can light the final beacon by themselves. Therefore, they steal the Mars Star from Felix and proclaim that it is time for him to die. On the subject of Felix's parents, the duo claim that Prox will release them as promised once the seal on Alchemy is broken, but Karst takes sadistic pleasure in exclaiming that the parents will just have to live at Prox regardless if Felix is not alive to take them to their home. Karst and Agatio attempt to murder Felix and Piers, but Jenna and Sheba arrive in time to back up their companions, and the duo are quickly outnumbered.

This battle may result in two in-game outcomes with follow-up scenarios. If Felix's party manages to defeat the duo, the Mars Adepts seem to accept their own deaths and tell their enemies to finish them off. Karst, however, suggests that Prox may retaliate by killing the captive parents if she and Agatio meet the same fate as Saturos and Menardi. Whichever way Felix is inclined regarding letting the duo live, Alex suddenly steps in and attempts to impress upon Felix what it would mean for Felix personally if Karst is not bluffing. Alex heals both Mars Adepts just enough that they can escape Jupiter Lighthouse with him using the elevator; the Mars Adepts are hardly grateful that Alex will not help them defeating the Adepts instead.

If Felix's party is the side that gets beaten nearly to death, Karst remarks that they were also shockingly powerful, and she exclaims that "treason deserves death" to justify her desire to kill them all now. When Alex arrives to tell them that there is "no time for petty grudges," Karst accuses Alex of having betrayed them and declares he ought to die too, but Alex tells the thoroughly exhausted duo that they are in no condition to fight either him or Isaac's incoming party. Forced to recognize their own circumstances, Karst and Agatio have no choice but to escape with the elevator. Regardless of whether this or the other scenario is considered the canon one, Karst and Agatio later part ways with Alex off-screen, perhaps more than content to do so.

Defeat at Mars Lighthouse
Despite having been denied her opportunity to kill Isaac out of revenge, Karst and Agatio make the best of things by heading back toward Prox to light Mars Lighthouse with the Mars Star and finish the quest Menardi pursued. Once they make it back to Prox through undisclosed methods (given that the sea route back into the Northern Reaches remains blocked off by ice), they tell their people that Felix "ran away" because the quest was "too dangerous," and they soon depart for Mars Lighthouse as Prox's strongest warriors remaining. However, as they wander aimlessly through the labyrinth, they are approached by the Wise One, the eye-like being that originally tasked Isaac with preventing the activation of the four Beacons. The being deems both of them to "lack the will to go any farther," possibly unilaterally, and suddenly transforms them into crazed and mindless Flame Dragons and seals them in a prison of ice.

Later, Felix's party, whom Isaac's party has since joined forces with because they had heard from an oracle that Karst would fail to light the Mars Beacon on account of a "powerful force that does not want to see Mars rekindled" barring her way, enter Mars Lighthouse in search of the Mars Star. They find the two creatures and free them from their icy prison, and the dragons immediately attack the party as if driven by instinct. Once Felix defeats the two beasts, they suddenly transform back into the battered and dying forms of Karst and Agatio, who do not remember the battle and comment that they now feel the cold of the weather in spite of what should be the Proxians' immunity to cold. They realize that they are about to die.

Karst and Agatio then become aware of Felix's presence in the room and, in stark contrast to the antagonistic stance they took toward him up until now, beseech him to take the Mars Star and light the Mars Beacon with it. As Felix agrees to do so on their behalf, Karst comments that she had forgotten that "people have such warm hands," and Felix's party has no choice but to leave them behind to search for and reach Mars Lighthouse's aerie. The two Mars Adepts struggle to stay alive until they have seen that the Mars Beacon is lit — which eventually does happen... but only after the Wise One puts Felix and Isaac's party through a horrific personal ordeal first.

Thanks to the breaking of Alchemy's seal and the releasing of elemental power throughout the world, Prox — and the rest of Weyard by extension — are saved from eventual annihilation. The people of Prox are grateful to the young Adepts for saving both their village and the entirety of Weyard, and they are regretful both that they had to hold the parents captive to spur on Felix's involvement in the quest and that Karst and Agatio, whom they admit were "a little obsessed," are gone as well.

As a boss in
Karst makes her sole in-battle appearance as one of a pair of boss-style enemies fought together in one battle at the end of Jupiter Lighthouse late in the game, accompanied by Agatio.

This battle is scripted to play out after a cutscene that takes place once you choose to cast the Jupiter Star into the opening at Jupiter Lighthouse's aerie. Among boss encounters in the GBA duology as a whole, this sequence has several unique features. First, you must fight two rounds against them with just a party consisting of Felix and Piers, and a cutscene will then interrupt the battle where Jenna adds herself back to your party. A second two-round battle takes place, and then the fight is interrupted again with Sheba's arrival and addition to the party. Then, the actual "boss battle" takes place.

There is no point attacking Karst and Agatio until Sheba has joined because they will refresh their HP between cutscenes, so you might as well stay healthy and defend to put your party in a good starting position when the real battle begins. Note that if both Felix and Piers are somehow knocked out during the first two-round phase, the cutscene where Jenna joins still happens, and the next two-round phase occurs with both of them defeated and only Jenna actively battling. If she is also somehow knocked out before Sheba can join, her joining happens anyway, and the real battle begins with her being the only one not to be knocked out.

Unlike most other boss battles in the series, the player is free to lose this battle without interrupting the plot. Losing will give a different version of the post-battle cutscene, but Felix's revived party will be allowed to proceed back out of Jupiter Lighthouse like normal. That said, winning the battle is preferable because the party will gain heavy EXP and Coin rewards, and the first available Dark Matter in the game will be dropped.

Of the two opponents, Karst does less damage overall than Agatio, but players prefer felling her first because of her lower HP and several available means of undermining the party, which her high agility helps her put into effect. Her Djinnfest skill puts one Djinni on each combatant into a one-turn Recovery session, likely lowering their class stages, and she has access to the Break Psynergy to deny the party's efforts to apply Attack and Resistance buffs and the like. Most notably, she shares Menardi's "Death Scythe" (originally "Death Size" in the first game), potentially downing the target regardless of damage dealt. Even if you would focus on felling Agatio first, be sure to have one boss felled before the other as soon as possible, since the remaining boss will become much easier to manage for the rest of the battle.

Karst is especially likely to be affected by Defense-lowering effects. Her statistics are as follows:

Karst uses the following battle commands with :

Trivia

 * Each of the three Golden Sun titles' primary villainous man-and-woman duos share their own thematic naming conventions. Karst and Agatio appear to be named after geology concepts, with Karst named after karst topography (where subterranean cavities can form within dissolving bedrock) and Agatio named after agate, a particularly colorful variant of crystallized silica.
 * Though Karst and the game itself thoroughly establish her obsessive focus on killing Isaac, when the opportunity finally arrives for her at Jupiter Lighthouse in the form of a two-on-two fight between her side and Isaac's, Karst is shown dueling Ivan while Agatio is shown fighting Isaac separately. One way to reconcile this seeming inconsistency with her stated characterization is to imagine that the Mars Adepts still retain the presence of mind to avoid matching their weaker warrior against their stronger opponent. Agatio's strength is described as second only to Saturos, and Isaac is depicted as the most powerful of his party, so Karst focusing her assaults on Ivan is the more pragmatic approach she could have chosen.
 * When Karst and Agatio are waiting at the aerie of Jupiter Lighthouse for Felix and Piers to cast the Jupiter Star into the well, both have hidden lines of mentally conveyed dialogue that cannot be seen through normal gameplay because the Mind Read Psynergy is currently inaccessible, which is thanks to Sheba being temporarily removed from the party. If a hacking device is used to give your smaller party mind-reading capability, Karst is revealed to be thinking, "Once Jupiter is lit, we'll have no need for you. Just watch..." It is unknown why this text would even be coded and written this way because it is established in-universe that Adepts can detect when the Mind Read Psynergy is being used to peer into their thoughts — such as when Karst herself responds to the player's attempt to Mind Read her during her debut appearance at Madra.
 * Similarly, in the epilogue sequence at Prox, when Isaac and Felix can talk to each of the citizens before leaving, all the citizens have hidden strings of Mind Read-accessible text that cannot be displayed because the two protagonists do not have access to the Mind Read Psynergy between themselves. One of these thoughts indicates that Karst and Agatio are apparently understood by the villagers to have been "defeated by a monstrous dragon" that Felix subsequently beat, which is a far cry from what had actually happened — that the Mars Adepts themselves were transformed into monstrous dragons that Felix had to put down.
 * In Golden Sun: Dark Dawn, the Psynergy Training Grounds obstacle course played through early in the game has the player shooting Fireballs to burn posters of Karst and Agatio, which represents Felix's original fights against them.

In fan circles
Karst certainly eclipses Agatio in popularity, and perhaps all antagonistic man-and-woman pairs seen throughout the series, because she is given a sympathetic and relatable motive rather than treating her role as just an obligation. Her desire to avenge Menardi by seeking vengeance against Isaac is seen as quality fodder for character drama. This positive appraisal of Karst is further strengthened by the character development she displays when she lays dying near the end of the game, where she personally asks for Felix to finish the quest for her despite having tried to kill him earlier in the game.

Naturally, there is a genre of fan fiction pairing her with Agatio, "Dragonshipping", though fan fiction authors have trouble coming up with convincing material to explain how Agatio and Karst could have any romantic chemistry between each other. That said, there is still an effort to interpret the duo's relationship as anything other than purely professional, so they are often depicted as longtime friends.

Perhaps the more popular shipping genre for her is between her and Felix, in what is called "Duskshipping." Authors are allowed to imagine a wide range of interactions between her and Felix during the latter's three years spent at Prox since before Saturos' main quest begins at the start of the GBA duology. Her imminent death scene is commonly cited as evidence that a romance between the two would be plausible because of what happens when Felix talks to her again; she responds as though Felix had placed his hands on her, and she remarks that his hands are "so warm."

Some fanfics like to portray the wave of energy that helped revive Felix's parents at the aerie of Mars Lighthouse a short time later as also having reached Karst and Agatio deep in Mars Lighthouse's inner depths, allowing them to just barely survive.