Tōhōshinki Arc

The first story arc in the Beelzebub series. The Tōhōshinki arc consists of Chapters 1-40 in the Manga and Episodes 1-22 in the Anime, and introduces the main characters and several other supporting characters. The arc also details Tatsumi Oga becoming the adoptive father of Beelzebub IV, the son of the Great Demon Lord sent to the Human world in order to destroy humanity.

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

Introduction
A young delinquent teenager, Tatsumi Oga, is sitting in the bedroom of, and with, his best friend Takayuki Furuichi while trying to tell a story. There is initially an interruption with the story-telling after Furuichi suspects that Oga is trying to fabricate some of the plots, resulting in a brief scuffle between the two, but Oga then continues to tell his story.

In a flashback, it shows Oga having finished beating up a group of teenagers and then asking them to bow before him. They oblige and then ask for forgiveness, apologizing for having attempted murder on Oga while the latter was sleeping. Oga brushes off their pleas and proceeds to drown one of them in the nearby river (claiming he was doing some "laundry"), before noticing a muscular man float down the river. Oga pulls the man ashore and the latter suddenly splits into two, revealing a green-haired baby. Oga thinks of options he can do about the current situation and tries to help the baby, twice, to no avail. After putting on an evilish face, the baby suddenly becomes attached to Oga.

It is then revealed that the baby is still with Oga in the present timeline, having followed the delinquent. Suddenly, a woman dressed in elegant Gothic clothing enters the bedroom through the window by riding her Ak-Baba. She demands that Oga hand the baby to her, to which he denies, creating an argument between the two. The baby suddenly sends off an electric shock after listening to the two argue, causing the woman to apologize and officially introduce herself and the baby: the baby is a Demon Lord named Kaiser de Emperana Beelzebub IV and she is his Demon Maid, a wet nurse named Hilda.

Hilda then proceeds to give Oga and Furuichi a better explanation of the situation. Beelzebub (also known as Baby Be'el) was sent by his father, the Great Demon Lord, to the Human world in order to destroy humanity. His father was originally supposed to do the destruction himself but do to his busy schedule, sent his son instead.

Oga is then told that he must take responsibilities for his actions, as Be'el is now seemingly attached to the Human delinquent. He denies to become a parent and Hilda, realizing that he won't live up to his duties, tries to kill him and Furuichi. This causes a massive explosion in the house, resulting Oga and Furuichi to run away for safety. Hilda catches up to them, however, and from the angled distance between the three Furuichi then comments how he can see up Hilda's skirt, provoking her and causing her to get Aka-Baba to attack them.

Eventually, the three come across an overhead power-line where a group of teenagers recognize Oga from Ishiyama High School. Meanwhile, Hilda cuts Oga's cheek with the sword hidden under her parasol and the blood falls upon Be'el's cheek. The teenagers realize that Hilda is attempting to kill Oga and are thrilled by the news. They then try to assist Hilda in hopes of gaining popularity. Be'el starts crying, however, and electrocutes everyone including the teenagers. His cry is enough to even send Hilda flying back when she attempts to calm him down. When things begin to turn sour Oga simply places a hand over Be'el's head and calms the latter down, then turning to walk around. A steel tower begins to fall over Be'el however and Oga protects the baby. However, he then passes out.

The next day, Oga wakes up and thinks that everything was a dream. Much to his shock, it was actually real: Hilda and Be'el are sitting in his room, the former stating that Be'el will become a great Human-destroying Demon Lord.

Becoming the Demon Lord's Parent
Hilda, using her real name Hildegarde instead, introduces herself and Be'el to Oga's family, orchestrating a scene that makes it appear that Oga had impregnated her and became a father. While Oga refuses to take responsibility for a child he doesn't truly father, his family forces him to become a man and accept his parental duties (unaware of the actual truth). Eventually, the other delinquents at Ishiyama High School learn about Oga raising a young baby, Be'el. This is because that now that Oga is Be'el's parent, he cannot be more than 15 meters away from the Demon infant or else he'll die.

Oga soon finds himself reaching his breaking point and while discussing it with Furuichi, unexpectedly meets the "man who split into two at the river". The man is revealed to be Alaindelon, a Transdimensional Demon. Oga is angry at Alaindelon as he's responsible for burdening him with so many responsibilities but Alaindelon tries to explain himself. He states that the ideal parent of the future Demon Lord is tough, arrogant, sadistic, and brutal; these are all traits that highly define Oga. Oga then suddenly comes up with a plan to free himself from his troubles: find someone who can be a better parent for Be'el. He states that the plan will succeed as Ishiyama High is a school populated by delinquents.

Going forward with his plan, Oga then goes to meet a strong delinquent named Hajime Kanzaki in hopes that the third-year student would prove capable of raising Be'el. When Oga tries to explain things in a more understandable manner, Furuichi steps in and proclaims that he and Oga wish to serve under Kanzaki. Kanzaki obliges but only if they're able to defeat Takeshi Shiroyama, one of his most loyal subordinates. Oga quickly defeats Shiroyama and is granted permission to join Kanzaki's gang. Shiroyama, however, struggles to get up and claims that he can still fight. Kanzaki kicks him, saying that he has no use for the underling anymore, but Shiroyama continues to state that he can still fight. Having had enough, Kanzaki asks him to jump from an open window in the room but gets Oga to do it when Shiroyama apparently can't do so. However, Oga notices that Kanzaki isn't strong enough to become Be'el's parent and punches the third-year instead, sending him falling out of the window. Kanzaki is soon brought to a hospital by an ambulance.

Later during a rainy day, Oga awakens and soon learns from Hilda that Be'el is having his "blessed" annual urination, in which Be'el urinates clean water enough to sink an entire town. Be'el's constant urination soon becomes a problem and Oga tries solving it by getting him a diaper. While at the store, one of the employees find Oga and offer to get him diapers after recognizing the latter. The employee is Shintarō Natsume, one of Kanzaki's underlings. Natsume is impressed by Oga's abilities and comments how easily he defeated Hajime Kanzaki of the Tōhōshinki, though Oga doesn't understand what Natsume is saying, let alone know the delinquent. Hilda, who'd been standing in the store aisle, unsheathes the sword in her parasol and attempts to kill Oga after he seemingly fails to understand his responsibilities. She misses, however, and almost strikes Be'el. Oga catches Be'el before the latter can get injured (from falling on the ground too hard). After witnessing the act, Hilda decides to help and let Be'el urinate on the ocean.

When Oga goes to school the next day, he notices an unusual tattoo on his right hand. Hilda and Alaindelon, who followed him to the school, also notice the tattoo and explain it to him (and Furuichi) on the school rooftop. The mark on Oga's hand is the Zebul Spell, also known as the Crest of the Royal Family. Suddenly, Furuichi asks why a Demon Lord needs a parent if another Demon (i.e. Hilda) is already present. Alaindelon then explains that Be'el can only use his Demon magic with someone to help him utilize it, comparing his situation to how electricity needs to run on power lines. Therefore, there comes the need of a Human parent as they can fully access the Demon Lord's powers. Later on, the five decide to go to a pier. Alaindelon and Hilda talk about Oga and the Zebul Spell while Oga, Furuichi, and Be'el fish. As they fish, Oga makes a deal with Be'el: if Be'el doesn't cry anymore, he won't fight for whatever reason anymore.

Meanwhile, a young delinquent named Tatsuya Himekawa is given a picture of Hilda (taken from earlier that day) and he sends a group, Team Caras, out to capture and bring her to him. The group finds Oga but the latter escapes by swimming from the pier along with Be'el, having taken his vow seriously. Furuichi, now alone, is asked for Hilda's phone number by the delinquents but states that he doesn't know it, let alone whether Hilda actually has a phone. He then tries to escape through non-violence but one of the delinquents punches him, causing Hilda to come over. Before he can react, Furuichi is knocked unconscious and awakens in an abandoned warehouse along with Hilda, also unconscious.

Furuichi then notices the delinquents from earlier and one of them, the same one who knocked him out, pulls out a gun and points it at Furuichi. Himekawa then appears, however, noting that Hilda is very attractive. He also notices Furuichi and asks why he's there, to which he is told that the first-year is a friend of Oga's. Himekawa beats the delinquent and asks the now-awakened Hilda for her phone so that he can call Oga, but she responds that she doesn't know what he's talking about. Himekawa pulls out a gun and shoots at her, burning off parts of her clothes. Furuichi then offers his phone, wanting to help Hilda and himself, to which Himekawa obliges and uses to call Oga. He tells Oga to meet at his current location if Oga wants Hilda and Furuichi safe. As time passes, it appears as though Oga isn't coming though Furuichi denies it.

Suddenly, the members of Team Caras capture Alaindelon whom they note was unexpectedly weak. Alaindelon splits into two, however, revealing Oga and Be'el hidden inside him. Furuichi wonders if Oga's forgotten his vow, but Oga contradicts that he's not technically fighting anymore: he's about to kill.

Himekawa praises Oga and then asks if the latter would like to be his subordinate, even going as far as to try and bribe Oga. He claims that it will serve well in unifying the school. Oga bluntly refuses and, when one delinquent ridicules him for going against a Tōhōshinki member and the son of a conglomerate, kicks the underling and states that he doesn't even know Himekawa. Himekawa realizes Oga's strength and decides to challenge him on his own. Oga manages to land a punch on Himekawa, punching through the armor under Himekawa's shirt. Himekawa then uses an electric baton. Oga dismisses the shock as nothing compared to Be'el's cry. The Zebul Spell on his hand begins to extend across his arm, in the process.

Hilda then frees herself from her bonds, having pretended to be caught by Himekawa's underlings, and Oga then starts charging some of Be'el's electricity onto his marked arm. He punches Himekawa with the attack, causing the latter to cough up a lot of blood, and becomes victorious in the fight. Himekawa is then sent to the same hospital as Kanzaki's, even being placed in the same room.

Anime and Manga Differences

 * The scene where Alaindelon is floating down the river was toned down in the anime. In the anime, his head is only visible and an arrow pierces his throat. In the manga, parts of his chest is revealed and the arrow pierces his left pectoral muscle instead. He is also bleeding from the said area and from his nose.