The Wheat Sword is a fictitious weapon that was created by fans as a joke. It is supposed to be the strongest weapon in the game. A user at GameFAQs named RyuKenshin took the joke to the next level when he wrote a guide to "Obtain the Wheat Sword," which was actually submitted and accepted on the site. Since then, it has become legendary on various forums and is almost never a topic unseen on these forums. Possibly in response to Camelot's failure to release a Golden Sun 3 in a satisfactory amount of time after the release of The Lost Age, forum posters have attempted to entertain each other and expand the joke to encompass other "grain weapons of ultimate power" such as the Bread Hammer, the Grain Axe, and the Noodle Whip. However, these added weapons are viewed by all as being tacky attempts to leech from RyuKenshin's fame, and the board regulars have persuaded all the non-troll users to scorn these items and all topics relating to them.
The dubious guide that started it all is posted here in its final version before it was removed from GameFAQs:
 As a weapon
The Wheat Sword is a Long Sword-class weapon that is given the following statistics:
- +250 Attack
- Removes the 999 Attack limit on that character
- +20 Venus Power/Resistance
- +20 Mars Power/Resistance
- +20 Mercury Power/Resistance
- +20 Jupiter Power/Resistance
- Critical Hits Increase
- Unleash: "Dutch Farmer"
- Chance of Dutch Farmer hitting 1 time: 37%
- Chance of Dutch Farmer hitting 3 times: 29%
- Chance of Dutch Farmer hitting 6 times: 17%
- Chance of Dutch Farmer hitting 8 times: 12%
- Chance of Dutch Farmer hitting 10 times: 5%
 How to "obtain the Wheat Sword"
First of all, you would need the Laughing Fungus in your inventory in Golden Sun: The Lost Age, as well as having both pieces of corn from the two games in your inventory. (Note that the Laughing Fungus is not specifically used anywhere in the actual walkthrough; it just "ensures" some events occur properly.) Then, after using scoop in Lemuria to get the Bone, you would give it to the nearby dog, who will supposedly trade you "the seeds". Already it is verifiable that the Wheat Sword is a hoax, since the dog does not respond to your bone in the actual game, and there is no code in the The Lost Age game cart for any item resembling a seed other than the normal Bramble Seeds you randomly get from enemies. So, it is safely assumed that all the following instructions are based on fantasy:
Use the seeds at Prox (where exactly is not specified in the FAQ) to create a small plant that you can cast the Growth Psynergy on to create a vine, and climbing it will lead you to a hidden area with a "lost Proxean" in it, who will tell you about a cave in Lemuria and how to get there. Once you get in that cave you will find the "rare stone", and giving that stone to the healer in Madra will prompt him to give you four copies of an "item" named the Silver Goblet. You would then give one of each Silver Goblet to the Mayors of Madra, Alhafra, Daila, and Contigo (the last of which apparently doesn't exist in the actual game). Upon achieving that, in the Anemos crater near Contigo on the overworld an enterable cave location would manifest, and upon entering it you engage in a battle with The Lost Age's most powerful enemy, Dullahan, regardless of whether or not you already defeated him in the nearby Anemos Sanctum. You get a Small Jewel as a battle reward.
Now, even though there exists a glitch in The Lost Age that allows the travelling party to walk most of the overworld region where the original Golden Sun took place, none of the older locations from that game are coded into The Lost Age, so it would be impossible to successfully follow the next instruction of returning to Sol Sanctum and using the Small Jewel to open a "hidden door" (the FAQ does not delve into any more detail on this ambiguous part). Inside this room is the odd sight of Saturos and Menardi fighting each other, with you watching on the sidelines in a cutscene-style event. After both of them manage to kill each other, Saturos leaves behind "Saturos' Armor", and when you return to Prox to give the fictitious armor to the mayor of Prox he will give you the Bottle of Fire.
Go to E Tundaria Islet where the penguins Pengus and Pengulina are. Give the Bottle of Fire to either one of the penguins, and they will get angry and engage you in battle. After felling them, you would use the Bottle of Fire to trigger a cutscene where the penguin corpses are cooked, and the Cooked Penguin items are added to your inventory. Go to Alhafra to where the "hungry kid" is and give the penguins to him, and he would give you a unique Coupon. (Note that said kid only appears in Alhafra earlier in the game prior to when Briggs escapes from prison and the town on the ship, so completing this step near the end of The Lost Age would theoretically be impossible because by that time he has disappeared.) Use this Coupon at Contigo's slot machine just as you would with a normal Game Ticket, and apparently regardless of your performance you will always win an item the FAQ author calls the Super Potion.
This is where the FAQ's instructions become so wildly fantastic that the browsers of dial-up Internet users may automatically close out and terminate their sessions after displaying the FAQ's contents on screen for a lengthy period of time. Use the Super Potion on Jenna in your party and she will become "immortal", which could be an original status condition. And then somehow separate Jenna from the rest of your party so you play as her alone with everyone else following her behind, and engage in the game's final battle with the Doom Dragon. Either during the battle or after you slay it (which one it is the FAQ does not say), Jenna will fall into the Lighthouse's opening, and Isaac and Felix jump in after her. The latter two are transported to Crossbone Isle from the first game (which, as stated before, does not exist in the code of the Lost Age game cart), and they find out in a cutscene that Jenna has been kidnapped and locked up by the supposed "brother" of the boss Deadbeard, "Red Face". Engage in battle with him now.Dullahan, and is immune to Psynergy, Djinn effects, and Summon sequences. Kraden, up until now, is not a playable character, but he will appear in your party alongside Isaac and Felix for this battle, and he can cast a command named Philosophy to instantly fell Red Face with an infinite amount of damage that qualifies as a standard physical attack. You win the key to Jenna's cell and a Utility Psynergy item named the Time Cube, which bestows the Time Travel Psynergy on whoever it's equipped on. After freeing Jenna, you would use Time Travel to travel back in time many years and go to Lemuria. Piers will be found here, and he will give your party a strange locked box. Cast Time Travel again to return to the present, and return to Madra so everyone in the normal party can regroup.
Give the box to your modern-day Piers, and in a cutscene he will remember that there is a cave under his uncle's bed in Lemuria. Go to Lemuria and that cave and you will meet the Lost Lemurian, who gives you the Super Lucky Medal, and you use it at Lemuria's fountain just like a normal Lucky Medal. If you land the Super Lucky Medal in the center to win, you will get a portion of the Wheat Sword called the Hilt of Fields (what happens if you don't win this round is not specified in the FAQ). In a cutscene, Garet will get angry over the fact there isn't a blade on this weapon, and throws it into the ocean in some way. A "mermaid" appears and casts a unique Utility Psynergy effect called Bubble on your party, allowing them all to explore Weyard's underwater portion. Very near your position is the Mermaid Queen's Chamber, with two guards at the entrance; to gain entry, Mind Read the guard on the right and tell the guard on the left what the right guard was thinking. In the cutscene to follow with the Mermaid Queen, she gives you the Coral Key.
Return to Mercury Lighthouse, and use the Coral Key to open a locked door that nobody playing the first game would supposedly see, and you will find the Mercury Star in its chamber powering the Lighthouse's beacon. Take the Star for yourself, and the beacon dissipates. Then Alex Teleports into the room, exasperated by what your party is doing, and demands you return the Mercury star. The FAQ is unclear whether this next step takes place in a cutscene or in battle, but it is apparently up to you to make Garet cast Pyroclasm and Jenna cast Serpent Fume (not the more powerful Dragon Fume, incidentally). Alex will be "crushed" and defeated, and you take "Alex's bag of things", and leave the Mercury Star next to him as you leave. Inside the bag is several Keys.
In the code of the actual game of Golden Sun: The Lost Age, there is a tile of wall in Anemos Inner Sanctum that the developers missed applying the collision detection for, meaning you can effectively walk through the wall to the black void outside the room. The FAQ "explains" why this glitch was committed by giving the next instruction of using the key in front of the offending wall tile, and a portal will appear for you to go through. You will reappear on the bottom of Gaia Falls (the FAQ author is obviously making a huge speculatory assumption here), where there is an alternative world to Weyard where "humans are evil and monsters are good". A Vermin will approach and speak to you in a cutscene, and it will give you the Hilt of Fields Garet threw away earlier. Garet still dislikes the fact there's no blade on the hilt, but in a cutscene Isaac uses Venus Djinni Ground to immobilize Garet and Sheba slaps him in the face with the hilt. Then the party somehow returns to the normal Weyard, but the FAQ completely neglects mentioning this step.Obaba in Champa, and in a cutscene she will tell you to find "the other piece" without giving any further instructions or hints. Then go to Golden Sun's city of Tolbi, where Babi's advisor Iodem has taken over his late master's position. Return Babi's Cloak Ball and Iodem will give you "Babi's Chest". Use another key within Alex's bag of things to gain the High Quality Flour. Take the Flour to the man in Contigo from whose stand you took one of your two pieces of corn. He says he only has one corn left, but he will trade you the corn with Alex's bag of things. With three Corns and one High Quality Flour in your inventory, bring them to the blacksmith in Yallam, Sunshine, and he will combine these items into one item called the Wheat Metal. This is the metal that is the "other piece" Obaba referred to, and now that you have both the Hilt of Fields and the Wheat Metal you can go back to Champa.
A climactic cutscene occurs at the entrance to Champa to signify the end of the Wheat Sword subquest. Feizhi will await, and point out that Felix did not give her Golden Ring present to Isaac. Feizhi assaults Felix, then gives Isaac the "Mythril Gloves" along with a kiss, to Jenna's chagrin. After Feizhi leaves and Jenna is done slapping Isaac, they go to Obaba while Felix is left on the ground. The Hilt of Fields and Wheat Metal are thown into the forge, and the Wheat Sword is created at last. However, Isaac cannot wield the sword and drops it, and the same thing happens with everyone else in the party, but Sheba figures out that the wielder of the Wheat Sword must also be wearing the Mythril Gloves that Feizhi just gave them, and Jenna takes the sword and the gloves for herself. Just then, Alex teleports in again, demanding to have his bag back, but Jenna defeats him in one fell swoop with a single swing from the Wheat Sword, to everyone's exclamation. Felix has regained his posture at this time, and Jenna gives Felix the Wheat Sword and Mythril Gloves for him and others to equip and use for the rest of the game. They leave Champa as Alex is left on the ground.