MangaDex

Maou Gakuen no Hangyakusha

Yuuto is an ordinary high school boy who, one day, notices a mysterious tarot card by his bed. He shows it to his parents, who give him the good news - as the son of demonking, he is eligible to become the next Demon Lord. As such, Yuuto is soon brought to a demonic academy in order to improve his devilish skills and earn the title of demon lord. And, you know, get a harem along the way.