You're the child of a powerfull god, but you live your life normally as a high school student. By the curse of the destiny, for some reason your blood was intertwined with a feared infamous demon king, who is hated by the gods. Because of that, everytime you get hurt or anything like that, it affects the demon lord. If you die, he dies too. Because of that, now youre under his protection, even tho he hates you.

"Who am I, you ask? Doesn't matter. You belong to me now. Do not dare get hurt."