Tatsumi Oga, a delinquent student at the worst high school in Japan, arrives at school with a small baby who emits massive shocks of electricity whenever it cries. Oga claims he found after splitting open a strange man who came floating along the river, though his friend Takayuki Furuichi doesn't quite believe. Whilst at Takayuki's house, they are both approached by a demon woman named Hildegarde who claims the baby, known as Kaiser de Emperana Beelzebub IV, is the son of Devil King who was sent to Earth to find a human to raise him so he could destroy humanity.

Furuichi is woken up by Alaindelon at 4:00 A.M. and is teleported to Ishiyama High to watch Oga and Tojo's fight with Hilda, Lamia, and Forcas Rachmaninoff. Meanwhile, Kanzaki, Himekawa, and Shiroyama confront Aizawa and Karou and begin to fight, but are quickly beaten by them, but they refuse to give up because of their stubborness. Natsume shows up and defeats Karou in one blow, and is about to deal with Aizawa. Kunieda and the Red Tails finish dealing with the delinquents and go to watch Oga and Tojo's fight, with Oga at a disadvantage. Beelzebub activates the Zebul Spell, thinking Oga cannot win, shocking everyone. Lamia accidentally sets off one remaining firework and it's aimed at Oga and Tojo. Oga easily stops the firework and causes a giant flaming Zebul Spell to appear on the ground. Oga orders Beelzebub to not interfere in his fight, promising he will win and Beelzebub erases the Zebul Spell. Oga and Tojo resume their fight, which goes on until dawn, and just as it looks like Tojo is about to win, Oga spins around and performs a suplex on Tojo, winning the fight. Oga tells Beelzebub he won the fight and Beelzebub tackles Oga to the ground. Tojo's past is revealed, showing a man he looked up to who taught Tojo the ture meaning of fighting and had a Zebul Spell on his shoulder, which Tojo got tattooed on his shoulder in order to look like him, and Tojo tells Oga he is now the strongest at Ishiyama High.

It begins with a bunch of Ishiyama delinquents crying and mourning over the loss of Oga and Baby Beel. Their tears stop short by the river when Alaindelon cruises like a speedboat and Oga and Beel pop out of the man.

At Oga's house, Hilda explains that the Great Demon Lord has no interest in destroying humanity which means the goal of raising Beel to destroy all humanity is no more. Beel and his gang will have to go home, and mass hysteria follows.

Will Oga, Beel, and the gang part ways forever?