Tatsumi Oga is a first year student in Ishiyama High School, a school for delinquents, where he is called the “strongest juvenile delinquent”. One day while sleeping next to a river, Tatsumi sees a man floating down it. Tatsumi pulls him to shore and the man splits in half, revealing a baby boy. This boy, Beelzebub, is the son of the demon king, and Tatsumi, along with Beelzebub’s demon maid Hilda, has been chosen as the one to raise him.