You start out with a cutscene. All of the Nintendo characters are standing on the edge of a cliff, looking at Galeem and his/her army of master hands. Galeem becomes a black hole and sucks in all of the master hands, then explodes, and the light that comes out corrupts all of the characters except for Kirby. We then see Mario tied up, with red eyes, slowly getting covered in yellow goop, and gets cloned. Then the cutscene ends.
Then you (Kirby) is on top of a hill. You need to walk down the path and beat your first opponent (Mario). You start out with some kind of samurai as a primary spirit.