Sora will once again be the protagonist of the game. The game will also see the return of Riku, Donald Duck, Goofy, and King Mickey, as well as the inclusion of familiar Disney characters. Sora, Donald and Goofy will attempt to search for seven guardians of light and the "Key to Return Hearts," while King Mickey and Riku search for previous Keyblade wielders, in an attempt to stop Master Xehanort's plan to balance the light and darkness. The game will feature new and familiar worlds based on Disney properties.
Source: Wikipedia, "Kingdom Hearts III", available under the CC-BY-SA License.