The Demon’s Dealbreaker by Delaney Rain

A witch, two fairies, a minor god, and four demons walk into a bar and suddenly Dwyer Eamonn’s life will never be the same.

Turns out that Dwyer’s parents promised him—their firstborn—as payment when they made eight different deals with various supernatural beings. At the stroke of midnight on his twenty-first birthday, every single claimant comes calling, ready to make Dwyer their heir.
Unable to deny them all, it’s up to Dwyer to choose which supernatural being he wants to become by spending time with each of them. What does a witch do all day? Do crossroads demons really hang out on street corners? He has eight hours to learn about them one at a time before he must make a decision.
Right away, one of them draws Dwyer in like no one ever has. He doesn’t want to become a demon, but he does want to be with one. Is that even possible? And since choosing an heir means these people want to shuffle off their mortal coil, is love reason enough to make one of them stay? After all, they’ll have forever once Dwyer makes his choice.