A pokemon/FF tactics sort of mashup would be quite cool in a TTRPG format if you were going the combat route.
As Gwathdring and others have mentioned even cooler would be more adventure pals approach. Whatever you favourite critter is you pal around using your combined abilities, maybe you can make a few friends along the way, or maybe it's more about customizing the training path to suit your play style.
Something like, "Rescue Monsters", you're a monster handler on a search and rescue team, and instead of dungeon crawling to kill baddies you're doing the same thing but rescuing injured/stranded heroes. Each member in the play group could a different role/monster pal. Heck, if you had a dual-character creation system where you build up both yourself and your chosen monster throughout the sessions... my oh my, I'd fund/buy that right now :-D