Tatsumi Oga was your average brute delinquent; probably the most ruthless kid at Kata Middle School, which in itself is known for its juvenile cases. How ruthless you ask? Well if you go to the third floor of the main building, and find the halls are lined with people with their heads stuffed in the walls and ceilings, you've entered his domain. One day, Oga was skipping school, fishing at a river, when this heavily built man floating in the river, he helps him out of the river, and then he literally splits in two! Out of the man comes a moss-haired baby, who then fixates himself on Oga's head. Then out of the blue, this woman arrives and provides explanation to this otherwise unexplainable issue. Apparently, the Devil King himself sent his son to Earth to find a host, and then with said host, destroy the world. Now in a situation that he can't find himself getting out of, can Oga take care of a child and avoid unnecessary trouble at the same time? Better for his own ideals, can he find a way to get rid of Baby Be'el?