He's a prince that was transformed into a cat by the evil bull at the all you can eat steak buffet restaurant, in Wario Land 5, he must traverse a food Pyramid, each passage based off a food group from the food pyramid mirroring the gem passages...
I never played any of the Mother games since I'm not big into RPGs, though I did play Undertale and I think it was alright. I've heard a lot of praise for every aspect of Omori apart from its gameplay so I'm gonna assume it's nothing to write...
And it's been done to death. Mother 3 was perfect, and Undertale was a great successor. But now almost every game keeps trying to do the same thing, and it's annoying as hell.
I still have no desire to ever play Omori and will never understand...