I mean you don't have to stick to undertale if you don't want to but maybe Fresh Sans would be cool to add, like you just encounter him ? I dunno. Maybe also horrortale. I think what also might be cool is like a side(?) mystery, you might already have that planned I have no idea but still. Though it might not work with what kind of story you are going for if you it's like just romance or fluff or something.
It was really good! I like it so far though I kind of got lost. I got what I needed for the very first quest and couldn't find my way back. I think I'm a bit dumb with the navigation but the game was pretty fun!
