Sora’s world is shattered when a violent storm hits his home, and he is separated from his two closest friends. The storm scatters the three to unknown worlds. At the same time, there is turmoil in the Disney Castle. King Mickey is missing, and Court Wizard Donald and Captain Goofy are out to find him. On their travels they meet Sora, on his own search for his lost friends. The three are told of ominous creatures called Heartless, being without hearts derived from an unknown dimension and are the ones responsible for the devastating storm.
The Disney villains, enticed by the power of darkness, manipulate the Darkness to help them gather the princesses of heart, who are needed to open a mysterious final door. Upon discovering the link between the Heartless, the storm, and the disappearance of King Mickey, Sora, Donald, and Goofy join forces and help familiar Disney heroes to save their worlds from the Heartless.
In Kingdom Hearts players step into the very large shoes of Sora, wielder of the keyblade. Sora can attack with the blade, and as he levels up he will gain more attacks that are automatically chained together. Sora can learn magic and put healing items into a quick menu, and both can only be used in real time. Donald and Goofy (as well as an additional character exclusive to each world/disney movie) will follow Sora. Their equipment and AI can be adjusted, but they can not be directly controlled. Defeated enemies will drop many kinds of items including synthesis materials. Sora can take these to the Synthesis shop in Twilight Town to turn them into usable items, accessories, and weapons.
Traveling between each world requires Sora’s party to fly through space in a Gummi Ship. The Gummi Ship can be completely customized, from speed and armor to weapons and shape, out of parts picked up from destroyed Gummi Ships, found in worlds, or bought from a store. Larger, more complex ships can be built as the game progresses, and plans can be found from destroyed enemies or from an NPC that will automatically build a Gummi Ship of specific specifications.