The story revolves around three Keyblade wielders in training: Ventus, Terra and Aqua. You have to play the story with all three characters to have the full story of the game. Since each of their story is so long (and it takes me a while to finish them) I’m going to make a different post on each story then do a short version timeline of who went where and when. Let’s start with the main focus of the story: Ventus
The game starts with Terra and Aqua taking the test to know who gets to be a Keyblade Master; it can be both of them, one of them or none of them. Aqua is given the coveted title, but Terra wasn’t able to fight back the darkness and is denied the title of Keyblade Master. Ventus goes back to his room and is faced with a masked boy that tells him Terra is changing and by the time Ventus catches up with him he won’t be the same. Ventus hurries outside to stop Terra from leaving, but doesn’t manage to stop him. Ventus decides to venture in other worlds to catch up to Terra.
He first visits the Dwarf Woodlands where he saves Snow White from the Unversed. With no news of Terra, Ventus goes to the Castle of Dreams where he finds himself in a tiny size. He pairs up with a mouse to find material for a dress for Cinderella.
After making Cinderella’s dress, Ventus travels to the Enchanted Dominion. There, he learns from the fairies that Aurora is in an eternal slumber caused by Maleficent and that her heart had been stolen. When Venus finds Maleficent, she tells him it was Terra that took Aurora’s heart. Ventus doesn’t believe Maleficent and battles with her. After defeating Maleficent, Aqua shows up and insists Ven returns home with her, but Ven still wants to find Terra so he refuses.
Ventus finds himself in the Badlands where he is faced with the masked boy again. Before being defeated by the masked boy, Mickey arrives and saves Ven. After the masked boy leaves, Ven learns that Mickey is a Keyblade Wielder in training under Yen Sid, but he ran off after learning the worlds were in danger. Mickey shows Ven the star shard he’d been using to travel between worlds and tells him how unstable it is. When he takes Ven’s hand, the star shard propels them in another world.
The star shard brings Mickey and Ven in Radient Garden. Ven loses sight of Mickey and finds instead an Unversed. After chasing it, Ven meets up with Terra and Aqua that had been chasing an Unversed themselves. The three of them fight the Unversed. After the battle, Aqua tells Terra that she had seen what he had done in the other worlds and that Master Eraqus wants him to go back home. Taking it as a sign Aqua had been spying on him, Terra refuses to go back home and runs off. Aqua then asks Ven to go back home, but he refuses again.
Ventus finds himself in Disney Town and helps Huey, Dewey and Louie to repair their ice cream machine. He then goes to the Olympus Coliseum where he meets Hercules and helps him train for the Games.
In Deep Space, Ven meets Experiment 626, who knew Terra and Aqua’s names and carried something that looked like the wayfinder Aqua had made for Ven and Terra.
Ven travels to Neverland where he hunts with Tinkerbell for a shooting star that apparently fell the night before. The shooting star was actually Mickey’s star shard, but Mickey was nowhere to be seen. As soon as Ven touches the star shard, he is whisked away in the Mysterious Tower.
In the Mysterious Tower, Ven lands in front of Donald and Goofy. Seeing the star shard, they think Ven knows exactly where their king is so they bring him in front of Yen Sid. Now knowing that Mickey isn’t travelling from world to world anymore, Yen Sid is able to locate him. Ven recognizes the Badlands and sets off to save Mickey.
Back in the Badlands, Ven finds Mickey but also finds Master Xehanort. Xehanort triggers Ven’s memories where he learns the masked boy is actually his dark side and that it’s Xehanort that separated them in the hopes of making the X-blade. Ven now knows that if he fights with Vanitas, the X-blade would be forged.
Wanting answers on who he is, Ven sets off to The Land of Departures to face Master Eraqus. Learning that Xehanort is still after the X-blade, Eraqus decides the only way of preventing this is to kill Ven. Terra appears and defends Ven by sending him off to Destiny Islands.
In Destiny Islands, Vanitas comes to fight Ven, but Ven refuses. Vanitas tells him to meet him in the Keyblade Graveyard where he could either fight or watch Vanitas kill Terra and Aqua.
In the Keyblade Graveyard, Terra and Aqua each fight on their side and both lose consciousness. Ven decides to end it all and fights Vanitas. After defeating Vanitas, they both end up in Ven’s heart where Vanitas finds a half-forged X-blade. He tries to fight Ven more so the X-blade can be fully forged, but Ven defeats him and finds himself in darkness.
We see Aqua and Ventus unconscious in space and Mickey coming to take their hands and bringing them somewhere. Then we see Ven in darkness and he thinks that place is familiar. Ven’s part of the story ends with him saying “This is your heart”.