Really fascinating game. The concept and take on the theme are amazing; it 100% could be expanded on. And the art is lovely, although the absence of a walking animation combined with the footstep sounds felt mildly uncanny to me for some reason.
I think the concept however is both this games biggest strength and its downfall. Getting the wrong character at the wrong time is just such a pain, and it feels really terrible if you get a character that you can't really use over and over again. To be honest, I don't really have an answer for how you would fix this though. I feel like taking away the randomness would take away from part of what makes the game unique and makes it thematically interesting (meaning its ideas about reincarnation in this case, not in relation to the jam theme). At the same time, it wouldn't be much of a metroidvania if the world was more navigable by all of the characters.
Anyway, I doubt you want design advice from me. Just some thoughts because this game got me thinking, haha. Overall, this is amazing work. If you do have plans to expand on this, I'd love to check out where you go with it! Really really cool!