How would you feel about putting Chara into another rpg format? melodiesoflife is Final Fantasy-inspired game that fits all your criteria (and I'd have to say the thorough and wonderful worldbuilding is a plus), wherein characters are given FF job class powers to try to stop the end of the world--but...! Given this is them, I imagine they might find it more interesting than really wanting to stop it... And I already feel bad for the monsters! We have a few players of morally gray characters who I know would love to see less goody-two-shoes types.

I've been waffling around the idea of apping an Undertale myself sometime! Muse decisions come hard though when the story is so rich you almost feel guilty about the idea of dividing your attention. 8Ia