Thalia Everhart is a kind-hearted former human who was chosen by destiny and transformed into a Charcadet to help restore balance to the Mystery Dungeon world.
When Ash faces and beats a trainer, he doesn't realize that the trainer is a witch and she turns him into a Zeraora. Now that he's a Pokemon, Ash and his partner Pikachu work together with some of his human companions along with some Pokemon to change him back to normal.
Everyone knows the stories, everyone's played the games, read the comics, watched the videos.
But maybe in order to save the pokemon world from an imminent cataclysm, what is needed isn't a human soul, but rather... a pokemon's itself?