So, Master Xehanort reveals that he has been literally shaving off the light in his heart with a plastic fork. Sora asks him why he would do this, because it makes him as unstable as a nuclear reactor run by
Homer Simpson, who is a boss in the Tron: Legacy world. Master Xehanort shows Sora the book D. I. Y. World Domination, which taught him everything he knew. Then Master Xehanort pulls Kairi out of his pocket and combines with her to form Kairinort. A boss battle with Kairinort commences, with the player controlling Sora and Riku, who are both fighting Kairinort.
After the battle ends, Pete appears to seal away Kairinort with his new keyblade (named "Whatdatfor"). Sora jumps in front of Pete's attack to stop him, and gets split into a new nobody and heartless as a result. The heartless is a four year-old Sora with a heartless symbol on his chest. Vanitas appears out of nowhere, grabs the heartless, and falls into a time hole. Riku decides to call Sora's new nobody, "Xaros". Meanwhile, Kairinort has revealed an even bigger castle hiding inside The Castle That Never Was.
Xaros and Riku head into Kairinort's giant castle to stop him/her/it. You play as Xaros and Riku climbing through Kairinort's castle, which contains Pizza Dream Eaters and random muggers made out of jello. You reach the floor with Kairinort, but it's only a cardboard cut-out and you're only halfway through the castle. Suddenly, Ansem and Xemnas show up, and declare that they want to "have some fun" with Xaros and Riku. Xaros defeats Xemnas, and Riku defeats Ansem, but Xaros decides to poke Ansem and gets possessed, turning him into some sort of Soransem. Soransem heads to the top of Kairinort's castle.
Riku gives chase, and sees that Xehanort has ten more incarnations. Young Master Xehanort is making them fight to the death, but when Riku tries to stop this, all eleven attack him. Suddenly, Vanitas and Sora's New Heartless appear, each ten years older. They beat up all the Xehanorts and literally send them crying for mommy. It seems they spent ten years in Twilight Town, where Vanitas turned into a pure-hearted hero and raised Sora's New Heartless as his own. He named the kid "Skyheart". Skyheart is a keyblade wielder and he has a distinct Marty Stu keyblade called Kingdomheartsword. You control Skyheart and Riku as you head again to the top of Kairinort's castle.
At the top, it's revealed that
Kairinort slept with Soransem and they had a kid Xehanort who can wield forty-two keyblades at once. Kairinort and Xehanort Jr run off to a hotel in The World That Never Was, pursued by Riku, Vanitas and Lea's brother Gee. Meanwhile, Skyheart fights Soransem, who has a new keyblade called "Shadowforge", and manages to kill Ansem while saving Xaros. Then Mickey appears and recreates Sora while keeping everyone's favourtie Stu Skyheart around. Skyheart and Sora pursue Kairinort and Xehanort Jr. Mickey goes home to watch TV.
Sora and Skyheart arrive just in time to see Riku defeating Kairinort and getting Xehanort Jr a mommy who isn't a zillion year old man. But alas, it was only a scene from the movie they were filming. Kairinort betrays Riku and keeps the profit from the movie for itself. Angered, Riku attacks, and Sora aids him. Meanwhile, Skyheart and Gee place bets while Vanitas single-handedly prevents an alien invasion.
Sora and Riku are about to finish off Kairinort for good, but then they are attacked by a random newcomer. It turns out killing Xemnas and Ansem again created a second Terranort in the realm of sleep, so Kairinort and Terranort the Second escape to hatch more evil schemes. Skyheart obviously wins the bet. He is a Stu after all.
Back in the real world, Sora and friends learn that Gee, Donald, Goofy and Sephiroth are all keyblade wielders. Skyheart is revealed to be force-sensitive, and Yen Sid says that he is the chosen one and the protagonist of Kingdom Hearts III. All the characters rejoice, including the original Terranort who decided to become a good guy.
Meanwhile, Minnie excuses herself from the festivities. A shot of her face reveals glowing red eyes and she is holding a book written by Xehanort called, "How To Be Xehanort". The words "To Be Continued..." appear.
The secret ending reveals that Yen SidXLarxene is the only canon pairing and the Ansem I was referring to the whole time was Ansem the Wise.
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