Tatsumi Oga is a delinquent that attends Ishiyama High School, a high school that is made up of only delinquents. He is uncaring and sadistic, usually inflicting as much pain as possible on his opponents whenever he fights. He cares for no one besides his only friend, Furuichi. Because of this, he attracted the attention of Beelzebub IV. The baby is attracted to evil, so he chose Oga as his adoptive father. Even when he decides to reform himself, he cannot help but have an evil, intimidating smile, even when he is trying to be friendly.
Major Story Arcs
Oga discovers a large man floating in a river. When he goes to inspect the body, the body magically splits and reveals Beelzebub IV. Beel is attracted to Oga's evil aura and puts Oga in a contract to be his adoptive father. Hilda, the Demon maid that takes care of Beel, unhappily accepts it and tells everyone that she is Oga's wife and Beel is his biological son as a cover, to Oga's discontent. The man in the river turns out to be another caretaker of Beel, Alaindelon, a transdimensional demon that carried Beel to the human realm. Still, Oga refuses to take care of the baby and goes around trying to find someone who is even more "bad" than him so that Beel will choose said person instead, leaving Oga free. He goes into the upperclassmen territories and runs into each of the Tohoshinki, the four strongest people in the school. Still, he defeats the first two members of the Tohoshinki. He runs into the female member of the group, Aoi Kunieda, who develops a secret crush on him. He is unable to find a suitable replacement until he meets the last and strongest member of the Tohoshinki, Hidetora Tojo.
The two get into a fight, at which Tojo shows that he is physically superior to Oga, and the two agree to fight again. During the second fight, Beel chooses Oga over Tojo, at which both seem content. After Oga defeats Tojo in a close battle, the demonic energy in his arm builds up and begins to swell. Hilda tells Oga that he would die if he didn't release the energy by punching something, so he punches the ground. Unfortunately, the punch releases so much energy that the high school is accidentally destroyed.
Saint Ishiyama Academy Arc
Because the school has been destroyed and is currently under reconstruction, its students are transferred to the high-class Saint Ishiyama Academy. In the academy, its students and teachers look down on the delinquents in contempt. Even the delinquents' homeroom teacher expresses his discontent at the delinquents. One of the students at the academy, Hajime Kanzaki, idolizes thugs and begs into becoming Oga's "disciple." However, things get worse when the Rokkisei (Six Knights), a group of students that enforce the rules of the school using force, begin a campaign to get rid of the delinquents by finding a way to expel them. When Tohoshinki member Kanzaki gets mixed up with the Rokkisei, he is easily beaten by one of its members. Some of the Ishiyama students are attacked, and they eventually fight back. The fighting escalates to the St. Ishiyama's rooftop, where the Rokkisei and some Ishiyama High students, including Oga, Tojo, and Aoi, skirmish for a bit before coming to an agreement. The two factions would hold a volleyball match during the academy's festival. If the delinquents win, they are excused from expulsion.
After having majorly-unsuccessful training for the match, the delinquents initially struggle against the Rokkisei. However, they find loopholes in the game's rules and start making a comeback. As the match goes on, they begin winning the approval of the audience and they finally pull off a victory with the St. Ishiyama students cheering them on. However, before they could celebrate, a rival delinquent school Teimo Tech invades the gym, led by Oga's old delinquent Reiji Kiriya, who has come to expel Oga to enact his revenge. He tries to get Oga to fight back so that he would be expelled, but Oga resists. However, when one of the Rokkisei, Miki (who has a connection to both Oga and Kiriya from the past), tries to fight back and gets beaten, Oga is triggered and scares off the Teimo Tech students and Kiriya with his demonic power. They tell the teachers and audience that the whole fight and demonic energy (including tatoos that covered Oga's body) were all part of an act staged for the festival. Both factions, now friends, go home, with none of them expelled.
Powers & Abilities
Oga, though originally not trained in any martial art, used to use his pure superhuman strength to brawl with his opponents before he met Beelzebub. However, he did pick up some wrestling moves, as early on in the series he is show using suplexes and elbow drops on his opponents.
Later on, Oga learned martial arts in the form of the Shingetsu style. With this, he is able to focus his energy into one point and can shatter boulders multiple times larger than he is.
He is seen keeping up with a motorcycle going about 50 kilometers per hour on foot, a feat that is beyond peak human.
After meeting Beelzebub, Oga acquired many demonic spells and abilities. He is able to project energy at his opponents from his hand, which is marked by the Zebul Emblem. The emblem allows him to manipulate the demonic energy given to him through his connection to Baby Beel. With this energy, he can destroy buildings, as shown when he destroyed the entire Ishiyama High School with a single punch into the ground at full power. He can also target enemies and areas with the emblem and trigger explosions at their location.
Oga has also developed a tolerance of electricity due to his constant electrocution by Baby Beel whenever the baby is upset. This is shown when he is unfazed by Himekawa's electric baton, which holds 12 million volts, which is stated to be enough to incapacitate a grown man for three days straight.
In dire situations, Oga can drink Beel's Super Milk to remove the barrier between him and the baby. This results in a great increase in power, strength, speed, and agility. His spells are at a much higher level in this form, being able to summon tens and tens of Zebul Emblems for a huge explosion. However, in this form, his personality and intelligence is reduced to Baby Beel's level. Also, if he uses the form for over 5 minutes, he will become trapped in that demonic form forever.