[AU]
You were a mermaid and mermaids were forbidden to mix with humans. When you were old enough to go up to the ocean, you saved a handsome man. A demon named Erwin decided to help you. And so, he turned you into a human. But here's the twist, in order for you to stay alive, you need to have sex as a life energy. So what will happen?
Adaptation of a manga. (Beware of sexual situations)
[EDITING]