Aoi and the Red Tails return to Ishiyama High to deal with Oga, despite not knowing who he is. When Takayuki drags Oga to meet her, Aoi is shocked to find Oga is the one she met at the park, although he doesn't recognize her back. Aoi starts to fight him using powerful bokuto attacks that cut through glass, but he manages to dodge all of her attacks. Impressed by her strength, Oga asks Aoi to become Beelzebub's mother which causes her to become embarrassed and run off. Afterward, Aoi seems to develop feelings towards Oga. Meanwhile, another delinquent gang plots to take down Aoi.

The Demon King sends Beelzebub some summer homework, containing a notebook which brings anything drawn in it to life. Next, Hilda brings Oga to Ishiyama High to collect prints of rare, powerful beasts, aka the delinquents, by whacking them with a giant fly swatter. During the chase, Beelzebub ends up planting several carnivorous Demon Plants, one of which grows into a massive giant causing havoc until Oga destroys it.

Oga and Furuichi accept Kazuya as their student, after being praised on how legendary they are. Kazuya tries to copy Oga to become strong like him, even making identical lunch boxes. Due to the Teimo incident, Oga and Kunieda meet Kido, the teacher in charge of student life at Saint Ishiyama Academy. They receive a warning of expulsion, should they persist to cause trouble for the school. Meanwhile, Kunieda tries to learn from Azusa to be more open to men, but realises it to be impossible. In order to get Kazuya off his back, Oga pretends to teach the secret technique of electric shocks, and manages to convince Kazuya successfully. Kazuya hears news of Azusa being kidnapped by a bald man suspected to be a Teimo member, and tries to rescue her with his new "powers". After Kazuya fails to land any hits, Kunieda arrives and reveals the man to be an acquaintance of her temple, and the situation is resolved.

Kiriya, the man who scarred Miki and tried to attack Oga in the past shows up at the volleyball match. He declares that he is seeking revenge on Oga, and has taken hostages at the school to stop anyone interfering. Kiriya reveals that he had to move away to Nara previously, and this is why he is only now seeking revenge on Oga. Miki, who also moved to Nara after being beaten by Oga, realizes that Oga had only beaten him to protect him from Kiriya when the two of them were both in Nara. Oga and Miki team up to take down Kiriya's henchmen while the 6 Holy Knights, the Red tails and the Tōhōshinki incapacitated all of the Keimo High students holding the St. Ishiyama students captive.

Oga begins his training with Ittousai while Furuichi and Lamia enlists the help of their Ishiyama classmates to search for Lord En. Can Oga and Beel complete their training in time and will Furuichi and Lamia find Lord En before he destroys the city with his army?

Oga ,Furuichi and their teacher (which was the Spellmaster) was searching for the black version of Baby Beel. Oga thought that it was so bored that it ran away. But actually it was because of Himekawa.They asked some girls if they saw someone with a baby, and they answered that they saw a nice looking, hot guy that smelled so nice. He took it because he believes that it was the key for their family to be more successful. In the end, Black Baby Beel was reunited with Oga's teacher.