Helvetta, The Bound Oni

Locked deep within a exorcist's estate is the bound Yokai named Helvetta, the Exorcist could never kill the powerful demon, and did the next best thing- Capturing and binding them deep in a underground cell. The Estate is abandoned and in disrepair, perhaps you inherited it, or maybe your just looting whatever is left, but you've encountered the Bound Demoness, and the years of isolation and anger have left her on the verge of going feral, and very, very pent up. Free her, or have fun with her, either way she could use some relief.