Sora, Riku, and Kairi build a raft with the intent to leave their home world of Destiny Islands to explore new worlds. On the night before the planned voyage, the Heartless attack the islands and Riku and Kairi disappear. Before the Heartless consume the islands, Sora mysteriously obtains the Keyblade, a weapon effective against them. Meanwhile, King Mickey has left his own world to deal with the increasing number of Heartless, leaving instructions for Donald and Goofy to find the "key" that will protect the worlds from encroaching darkness. Donald and Goofy use the Gummi Ship to travel to Traverse Town, where they find Sora after he wound up there following the destruction of his world. The three decide to travel together – Donald and Goofy to find Mickey, and Sora to find Kairi and Riku – traveling to various worlds and sealing their "Keyholes" to prevent their "heart" from being consumed by the Heartless.
The main battle party consists of three characters: Sora, Donald Duck, and Goofy. Sora is directly controlled by the player from a third-person camera angle. All other party members are computer-controlled, though the player can customize their behavior to an extent through the pause menu. Donald and Goofy comprise the party in most areas, but nearly every level features a character who may replace them. For instance, Jack Skellington can join Sora's party in Halloween Town, but can't accompany the player elsewhere. In some worlds, the party changes its appearance, has abilities unique to that world or both; the characters can fly in Neverland, acquire aquatic forms in Atlantica which enable them to survive underwater and gain Halloween costumes in Halloween Town to blend in with the locals.
Source: Wikipedia, "Kingdom_Hearts_(video_game)," available under the CC-BY-SA License.
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