He meets Donald and Goofy, and together they plan to visit other worlds to "lock" them to prevent the evil Heartless from conquering the universe, and find beloved King Mickey

The world that Goofy and Donald are from, their king, Mickey, has discovered a problem amongst all the worlds

whatever Goofy is, Sora journeys to all sorts of Disney worlds, and a few original ones as well searching for his lost friends and the missing King Mickey.

So with Sora being the Keyblade Master, Goofy and Donald decides to team up with him to help search for the missing King as well as to seal all the worlds

I won't spoil the plotline for you, but it begins with a boy receiving a strange blade and a search for a lost king

In the game you team up with Donald Duck, the Court Wizard of King Mickey Mouse, and Goofy, Captain of the Royal Guard