Tatsumi Oga arrives at Ishiyama High school with an electric emitting baby, whose origins he has trouble explaining to his friend, Takayuki Furuichi. They are then approached by a woman named Hildegarde who explains that the baby, Kaiser de Emperana Beelzebub IV, is the son of a demon lord and Oga has been chosen to raise it to destroy humanity. After initially being chased after by Hildegarde after refusing to take care of Beelzebub, Oga learns that if he can find someone more ruthless than he is, he can get rid of him. Oga seeks out one of Ishiyama's toughest delinquents, Hajime Kanzaki, easily beating his henchman, Shiroyama. When Kanzaki asks Oga to throw Shiroyama out of the window, Oga determines from Beelzebub's reaction that Kanzaki is not suited and knocks him out the window instead. That evening, Hildegarde arranges to stay at Oga's house, mentioning Beelzebub cannot go further than 15 meters away from him. The next day, another one of Ishiyama's feared leaders, Aoi Kunieda, arrives with her gang to face against Oga, though she recognizes him as someone who helped her at the park while she was in disguise taking care of her brother. After dodging her powerful attacks, Oga asks Aoi to be Beelzebub's mother, which just makes her embarrassed. Later, another leader, Tatsuya Himekawa, arranges for Takayuki, Hildegarde and Beelzebub to be kidnapped. Oga manages to catch up with the help of the transdimensional demon, Aldelaion, before utilizing Beelzebub's power to beat Himekawa. The OVA ends with Oga confronting the final leader, Hidetora Tōjō.