Whoops.
Sorry, that I'm replying about a week later.
I've been thinking about this idea quite a bit, and have been trying to expand on it.
I've come up with a few thoughts, for one of my characters she would go into the human world to retrieve supernatural heirlooms or artifacts, that had been taken to that side.
We could expand upon that idea, because there would probably be a whole unit - sort of like a police thing. The unit having to capture back wayward supernaturals, who go into the human world to cause havoc. There could be other cause for having to venture into the human world, for love, revenge; I guess anything really.
We could do a college type scenario, this over a highschool one as the college one would entail more classes/hands on field work.
We could explore the hierarchy of the supernatural world. I was thinking an olden family, generation to generation, has been the go to for everyone. If there's a dispute between families, they would settle it.