Prince En Arc

The Prince En arc is the fourth story arc in the Beelzebub series. In the Manga, it's comprised of Chapters 77-113 while the Anime adaption follows Episodes 37-50. This arc introduces Baby Be'el's older brother En and his three wet nurses, as well as Zenjūrō Saotome. This arc also details the introduction of Behemoth's 34 Pillar Division.

Synopsis
Spoiler warning: Plot and/or ending details follow.

The Contractor and the Demon Lord
Oga is walking to school with Be'el, complaining in his thoughts about how Hilda just suddenly left despite being Baby Be'el's wet nurse. He also thinks about how he hasn't learned anything about Izuma being a possible Demon. Oga then meets Aoi while walking, but the girl says nothing to him. Oga then gets to the school and finds himself surrounded by a harem of fangirls, all of whom are from the same fanclub that support him and Be'el. The girls are then shooed away by Miki. Aoi then appears and coldly greets Miki but again, says nothing to Oga. The Red Tail then appear and harass Oga for "staring" at Aoi and eventually leave, right after a barrage of insults. Miki then asks if he and Oga can walk home, to which Oga readily rejects. Oga then proceeds to class where Furuichi starts bragging about his own harem of girls, but Oga then starts to ponder what he should do.

In another section of the school, Hidetora Tōjō is shown talking to Shizuka Nanami of the Rokkisei about Izuma classroom, wanting to find and fight Izuma in a battle. However, Tōjō would eventually find Kaname Izuma on the school rooftop. Oga also finds Izuma there and asks Tōjō to leave, wanting to talk to the Horseman alone. Tōjō refuses and Izuma suggests that they all fight together. The three are about to start but then a mysterious man appears, having leaped up to the rooftop from the classroom below after hearing that they were about to fight. He stops them and defeats them all in less than a second. He drags Tōjō and Oga back to class, revealing himself to be Zenjūrō Saotome, as well as the new homeroom teacher for the Ishiyama class. The students are astonished that he could have defeated Tōjō and Oga so easily but Aoi is more curious about Takumi Sadohara and asks why he was fired (something that Sadohara also asks, albeit in the principal's office). However, Saotome simply changes the subject and starts to flirt with Aoi, causing the Nene Ōmori and Ryōko Asuka to get mad at him. Saotome then explains that Sadohara wasn't supposed to be permanent. Afterwards, he then leaves before Tōjō or Oga would awaken. When Tōjō awakens, he leaves to find Saotome but is unable to find the old man. He is soon approached by Shizuka, who then asks him about Saotome. Tōjō confirms that the man has returned.

Saotome is shown atop the roof of the gymnasium where the volleyball match had occurred. He complains how the Zebul Blast used to defeat Kiriya created a transdimensional portal, though he adds that the portal did reduce a high amount of damage that could have destroyed the school. Saotome's contracting seal expands around his arm and he punches through the portal, closing it off. Oga, Tōjō, Izuma, Miki, and Shizuka were all able to feel his Demonic magic. As the portal closes, Hilda suddenly appears and draws her sword. She asks if Saotome is one of Behemoth's men and when Saotome hesitates to answer, she strikes at him. She pins him down and questions his use of Demonic magic which he'd just used to seal the portal. Saotome ignores her and mentions how her underwear is white. Hilda realizes that he can see up her skirt and flusters, allowing him to escape. He then reappears behind her, groping and complimenting her breasts. She frees herself and Saotome starts explaining how he doesn't want to fight her. Hilda notices that she doesn't have to hold back against him and unleashes her own Demonic magic. She tells him to die and their fight ensues. She appears to have an advantage over Saotome until she summons a high amount of magic, to which Saotome then releases his own magic and captures Hilda with a powerful spell. Hilda is astonished, even more so when she notices the Zebul Spell on Saotome's arm. Saotome warns her that if Oga doesn't get stronger, he'll die. He then leaves the gymnasium's rooftop and is confronted by Oga. Saotome tells Oga that he's the delinquent's teacher and that he should go to school tomorrow.

As he leaves, Oga himself is confronted by Aoi. Aoi, dead serious, asks Oga about who Be'el really is. Oga tries to explain the situation to Aoi but cannot figure out how to do so, causing him to let Be'el explain things to Aoi. However, as Be'el is an infant he cannot say words properly. Furuichi, who was watching the three from afar, gets angry and starts explaining when Aoi asks if he knew about Be'el. However, Furuichi proves himself incapable of explaining things either. Be'el is upset that they can't remember and tries running away but a mysterious woman, dressed in the same clothes as Hilda, picks up Be'el and says the Demon Lord's real name. The woman is shown to be a splitting image of Hilda and Furuichi even asks if it's her, but the woman knocks him out for confusing the two. She also turns to Oga and attempts to kiss him.

However, Hilda appears and prevents the act from occurring. She also identifies the woman as Yolda. Hilda says that Yolda is after her and that they should leave, though Yolda objects saying that it's been hundreds of years since they last saw each other. Yolda even pulls her broom, flowing with Demonic magic, but is told by a wet nurse named Izabella to stop, who is with another wet nurse named Satura. Yolda and Izabella begin to argue but are told to stop by a young, green-haired boy with slit eyes. Hilda recognizes and identifies the boy as En, the older brother of Baby Be'el. Izabella summons a throne for En to sit on. En lounges on the throne and is enjoys being pampered by his wet nurses. Aoi asks what happened and Oga explains that it's magic, explaining further that Hilda is a Demon and that Be'el is a Demon Lord. En asks if she is Be'el's contractor but Yolda says that it's Oga, though Yolda does add how Aoi was upset when she tried to kiss him. Yolda then knocks Aoi unconscious. Oga is angered but before he can do anything, Hilda suggests that they go somewhere else to talk.

They eventually go to Furuichi's house, taking Furuihci and Aoi along with them. At Furuichi's house (the said resident now being awake), En and his wet nurses explain how the Great Demon Lord wanted to destroy humanity, but forgot that Be'el was already sent to do the job, and sent En to do the job. Oga comments on how random the Great Demon Lord can be and goes on further to even insult En, to which Yolda attacks him with her broom. Izabella then states that they're only there to extract information and Hilda then asks what will happen to them, now that En is to finish Be'el's job instead. She does not receive a proper answer, however. When En and his wet nurses decide that it's time to leave, the Demon Lord tries to say goodbye to his younger brother but Baby Be'el starts throwing ice cubes at him. En starts crying and causes the area around him to burn. His wet nurses try to comfort him but when all seems to fail, Satura requests that Furuichi bring En games. En starts cheering up and brags about how much of a game player he is. However, he doesn't recognize what a PS2 is and finds himself losing to a game of Biohusband 4 (a parody of the Resident Evil franchise). En decides to spend the next day playing various video games and prepares to leave with his wet nurses. Before they do leave, however, Izabella explains to Hilda that while they're fine with En and Baby Be'el destroying humanity together, whoever proves more powerful will be the rightful heir to the throne. One of the people supporting En in this campaign is also said to be Behemoth, a very powerful Demon. En warns them that Behemoth's men will be after them and that they should try to stay alive.