Taking place in a modern world where fantasy creature, which had remained hidden in myth and shadows, finally showed themselves to the humans. The news of this set the world on fire, the legends that people had heard about but not believing suddenly being reality.
After a while fantasy beings slowly started to mix with the lives of humans, living in the cities with them in plain sight, getting jobs and making friends. But with this the more sinister side of the Supernatural would also started to appear more.
Enter my character, a Incubus Detective that starts a private business in investigating crimes committed by the Supernatural. After he gets his business up and running, he finds he needs some help. And that is where your character comes in, having seen the ad for a female assistant to help in cases and also help with my characters Incubus needs, which have gone into overdrive now that he can freely move among humans himself, not having to hide in the shadows.
We can also do a story where instead of my character being a detective, he starts being a vigilante, helping fight crime the is supernatural. Your character can be a police officer, that teams up with my character secretly to solve crime together.
This is just a basic outline and if you want to change it more to liking, that’s fine.