Manga Maou Gakuin No Futekigousha

The story tells of a demon lord who got tired of his time and decided to reincarnate in the future. He, being an extremely powerful creature that can destroy any person, god or other creature, was not needed in the local magic academy, since no one needs a teacher of demon lords. As a result, the Demon Lord is in confusion, because he did not expect the whole world to soften so much, the forces of the creatures will significantly decrease, and everyone will continue to live in this world, getting soaked further.