Both Sora and Riku are fighting to stop Master Xehanort in Kingdom Hearts III. The series’ supervillain wants to start a war against the tyranny of light, which Xehanort believes will restore equilibrium of light and darkness.
Sora, Donald, and Goofy set out to search for the Seven Guardians of Light and the Key to Return Hearts. Meanwhile, Riku and Mickey are on a different quest looking for previous Keyblade wielders.
Square Enix wouldn’t confirm which worlds will be in Kingdom Hearts, but a representative from Disney said the game will feature worlds unseen in the franchise. I asked Shinji Hashimoto if Pixar worlds would be in the game and he said he couldn’t comment on the topic at this time.