The first game in a collaborative series between Square Enix and Disney mixing JRPG and the Final Fantasy universe with well-known Disney characters. The game starts with Sora, a 14 year old boy who lives carelessly on Destiny Island with his two best friends, Kairi and Riku. They seek to leave the islands to explore what they profetize must be just one of many Worlds out there.

While building their escape raft one day, their island is attacked and destroyed by creatures known as the Heartless, with Riku succumbed to darkness and Kairi's whereabouts unknown. Meanwhile, King Mickey has left his World in search of something unknown, and tasks Donald Duck and Goofy to find a "key". They meet with Sora in Traverse Town and finds out Sora is the wielder of the Keyblade, the only weapon capable of defeating the Heartless.

Together they form an unlikely party with Donald and Goofy on the quest to find Mickey and Sora to find his friends. To do that, they'll travel to different Worlds based on Disney films to uncover a large plot spanning both time and space.