The story starts off with the music video opening(pretty cool) It's basically a dream of Sora's. Riku is the friend that always has to compete with Sora. He's the more uptight one. Sora's more of the relaxed friend. They're also friends with Kairi who is the mayor's daughter. She actually came from another world but she doesn't remember. They're building a raft to see if they can go to other places. Wakka, Tidus, and selphie also live on the island. There's also some tension over Kairi between Sora and Riku. There's also a story thing with a Paopu fruit(a fruit shaped like a star). According to them, by sharing the fruit, the ones who eat it will have their destinies intertwined or something like that. I think it's more of a romantic type thing. Then one night, there's a big storm thingy with a black vortex. Riku tells Sora to go into it with him and they'll go to other worlds and may never come back again. Sora then gets sucked into a ground by a black smokey vortex. During this whole time on a different world, King Mickey has gone off to try and figure out why some of the worlds are disappearing and told Donald and goofy to go and find the keybearer and to give the person support. So Donald and Goofy go off in a ship made by Chip and dale to another world to find this person.
Back on the island, Sora is still on the island and it's breaking apart and he ends up fighting this giant shadow thingy that he fought in his dream. He finds himself holding a key shaped weapon for reasons unknown so far. He then goes to the secret place where there was a door and is able to go in. He ends up in Traverse Town where Squall, Yuffie, and Aeris is. Donald and goofy are there too looking for squall and the "keybearer." Sora ends up getting his butt kicked by Squall and they all take him to a hotel. Once he wakes up they explain to him that the reason that the heartless(evil shadow beings that steal hearts and I guess they don't really have a heart either), are following him because he has the "Keyblade." Sora then finds Goofy and donald and they decide to join for their own reasons. Donald wanted Sora so that they can find Mickey and Sora wanted to join them so that he could find Kairi and Riku. They get in a fight over the ship and end up in wonderland. Alice is being accused for attacking the queen and trying to take her heart. They go off to find clues to prove her innocence and the Cheshire cat helps them. They prove Alice innocent but the Queen wants to kill them anyways. During the whole fight, Alice gets taken but unknown ppls. They're going to leave when a heartless boss attacks them. They beat him and "seal" the heartless by Sora's Keyblade and the keyhole of the door.
They end up in Jungle world where they meet Tarzan and Jane. There's also Clayton who's there to kill the gorillas and make a profit out of it. At first Sora and Donald don't get along too well and try to go their separate ways. Clayton tries to find the gorilla breeding site but Tarzan won't help him. Then he somehow gets there and Sora and Co. go to fight them and Tarzan joins the party. Clayton has this giant chameleon that he rides on and attacks them. After that Sora seals the place and there's this cheezy thing about your friends and the heart.
There's also the Colliseum where hercules and Phil are. They have tournaments and there's this whole thing about finding out what it means to be a true hero. It's just there to fight tournaments and to get stuff. Sora and Co. get to fight Cloud who was hired at first by Hades because Hades promised that he'd help him out by helping him find a certain person. (At first I thought it was sephiroth but it was actually Aeris and personally, I REALLY hated her in ff7) Anyways, he gets beaten and hades gets mad and tries to get them with Cerberus. Sora and Co come out but go back in to help cloud, who's beaten up and unconcious, and Hercules who is saving Cloud. Sora and Co also get to fight Yuffie and Squall. Yuffie throws her weapon and shuriken(it annoyed the hell out of me) and Squall blasted fireballs and made his sword bigger kinda like one of his limit breaks. Also close to the end of the game Sora gets to personally fight against Sephiroth who REALLY kicks butt. He comes into the ring kinda like by a summoning type spell in ffX. He's fast and so far, me and my friend can't figure out a way to really hurt him. and he looks GOOD. anyways, back to the story.
Sora and donald and Goofy go to traverse town where they see Riku again. He tells Sora to join him but Sora gets distracted and Riku disappears. Then when they go in to see Squall and them Riku sees him talking to them and Maleficent tells Riku that Sora has abandoned him for new friends and that he doesn't care about Kairi so he should join them and forget Sora. Then they go to Agrabah where they find out that Jafar has taken over and that heartless are everywhere. Jasmine gets kidnapped so Aladdin and genie go to save her but the lamp gets taken away. So they all go to the cave of wonders to go save her. they find Jafar who tells Genie to beat up Sora and Co but they beat him and he makes his wish to be a genie so Sora and Co have to beat jafar b taking his lamp away from Iago. Once they beat him they find out that Jasmine has been taken away also so Aladdin frees Genie as a last wish and he joins the party as a summoned being.
At Traverse Town they get to go to the Wizard's place underground and Sora gets to be in a Winnie the Pooh story. The fairy godmother from Cinderella is there and she helps out by freeing the people stuck in the summoning gems. These are basically your summoning spells.
They then go to another planet but get swallowed up by monstro, giant whale from Pinocchio. Geppetto is inside with Pinocchio and he's a stupid puppet so he basically goes deeper into the whale. Sora has to go in and save him cause Rikku is being all creepy about it. He actually took Pinocchio's heart to try to save Kairi who had her heart stolen and is now a lifeless puppet.