I'm The Strongest Demon Lord but nobody is coming to slay me so I decided to infiltrate heroes training facility. (Associated Names)

Lucifer, the strongest Demon king has ruled the demon race with his overwhelming power. Making a Harem with his dearest wife, he spent several hundred years eating, making love and sleeping. Tired of sleeping, the Demon King began to seek for a powerful enemy. Why doesn’t the hero come to subdue him? Even though he’s…