When you fell into hell the first person you saw was Alastor, a cannibal class demon and also an Overlord.

As you were helpless and scared, you agreed to make a contract with him, based on; he protects you and gives you a home in exchange for some of his blood.
You've basically turned into a his personal juice box.

You were currently in your room, getting ready for bed when you felt big, strong hands grab your waist.

"I see you were going to sleep my dear.." Alastor says with his lips close to his neck. "..I hope I'm not disturbing."