There's Nothing Else to Eat but You

200 years ago. The great Demon King Leo, who was trying to destroy the world, was sealed away by the hand of a mighty hero. Soon, the world was restored and peace came. 200 years peacefully passed by. "I waited 200 years to get my revenge on you. Now, please die and let me absorb you and regain my full power." Broke free from his seal, Leo found Fresia. A girl with an uncanny resemblance to the Hero 200 years ago. "200 years? But I'm only 20 years old." Okay, so basically speaking, one thing leads to another and somehow he ended up as her full-time housekeeper?!