The story follows the strongest juvenile delinquent, Oga Tatsumi, he is a first year in Ishiyama High, the school for delinquents. The story starts as he is telling the story of how he found the baby to his best (and only) friend Furuichi Takayuki. One day while fishing by the river (actually, taking revenge on people trying to kill him in his sleep), he sees a man floating down it, he pulls him to shore and the man splits in half revealing a baby boy. This boy is the son of the demon king and he has been chosen as the one to raise it with the baby's maid Hilda. The story follows his life with the child and at the delinquent school.
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.
The delinquent group, MK-5, come to confront Oga, but are promptly beaten by him and Hildegarde, who catches the attention of a smitten Aoi. As Aoi's right hand ladies, Chiaki Tanimura and Nene Oomura confront Oga, Hildegarde, who had heard from Oga about his plans to dump Beelzebub onto Aoi, challenges her to a fight to test her strength. When Aoi returns to find Chiaki and Nene injured, she assumes Oga is responsible and confronts him in a fight. In actuality, Chiaki and Nene were attacked by MK-5, under the orders of Miwa, who desires the title of Queen. Shintarou helps Nene get to Aoi to tell her the truth, but when Miwa makes his move, Oga promptly beats him up. Afterward, Aoi is once again baffled by Oga trying to give her Beelzebub, explaining that he's forced to raise him because of Hildegarde. Later, Aoi decides to quit the Red Tails and put Nene in charge, feeling that she is no longer able to serve as their leader.Watch Now:Amazon
Himekawa plots revenge against Oga by setting him up with a poisoned sandwich, but it doesn't affect him due to his resilience to Hilda's cooking. He next attempts to use a popular costumed character in order to try and capture Beelzebub, but Oga and Beelzebub notice that he's a fake due to differently colored chopsticks. He later attempts to seduce Takayuki into giving him Beelzebub, but Alaindelon intervenes, transporting Himekawa and his gang to a far off island. The resulting failures leave Himekawa with no money to hire any more henchmen. Ans as he tries to attack Oga by himself, he gets caught up in fighting against a rival gang also attempting to kill Oga. Afterward, Kanzaki offers him one of his yogurt drinks, to which Himekawa repays him with a year's supply with a month long lifespan.Watch Now:Amazon
Oga's family coerce him into taking Beelzebub to the park so he can make his 'park debut'. Despite making a bad impression with the other mothers, Oga meets a girl named Aoi who is looking after her little brother, Kouta. Aoi tries to help Oga make his park debut which, partly due to the appearance of Alaindelon, doesn't reap much success. The general antics convince the other mothers to call over a police officer, who starts badmouthing both Oga and Aoi. Before Aoi can lose her temper, Oga throws him into a trash can, with Aoi coming off impressed. After Oga leaves, it is revealed Aoi's true identity is that of Aoi Kunieda, leader of the Red Tails gang and one of the Tōhōshinki.
The students of Ishiyama High settle in at St. Ishiyama, with all the significant characters being placed in the same classroom. Their new homeroom teacher, Sadohara, challenges Tojo to an arm wrestle to try to establish some authority over the class, failing miserably when Tojo accidentally slams him upside-down against the wall. He then picks a second target, Oga, who was sleeping in his seat, and wakes Oga in order to challenge him. Baby Beel is angry to have been woken and subsequently tantrums, shocking Oga and Sudohara. An aspiring delinquent from St. Ishiyama, Kazuya, goes searching for Oga after hearing rumors of his strength, bringing his childhood friend Azusa with him. A gang pick a fight with Oga and Furuichi in an alleyway, and upon fighting back, a gang member grabs Kazuya and Azusa, who were watching from the entrance of the alleyway, and threatens to hurt them if Oga does not submit. Aoi shows up and frees them, allowing Oga to now beat the gang senseless. As he's beating them, Baby Beel has a tantrum, electrocuting all of the gang members and Oga. Kazuya confuses this for Oga's attack. After leaving the alleyway, Kazuya begs Oga to take him under his wing.Watch Now:Amazon
As Ishiyama High holds an assessment test for its studyphobic students, the Great Demon Lord also holds a test for Beelzebub, requiring him to earn points by beating up various things, or run the risk of both he and Oga facing remedial classes in the Demon World. With Beelzebub not showing much hope, Oga decides to try and dump Beelzebub on whoever scores highest on the test. When a rival school interrupts the test, Oga fights them off to allow the other students to keep on the test, earning enough points to avoid remedial lessons, later learning that the smartest student it actually Takayuki. Later, Hilda prepares a letter to the Great Demon Lord, writing reports on Oga, his family and the Tōhōshinki.Watch Now:Amazon
Hildegarde presents herself to Oga's family in the wrong way, giving them a different view of the situation. She also informs Oga that if he is more than 15 meters away from Beelzebub, his cries may destroy the city. Whilst dealing with this situation, Oga comes up with the idea that, if he can find someone more strong and ruthless than him, he can dump Beelzebub on him and be free.Watch Now:Amazon
As the Zebub Spell is restored, Lamia and Dr. Forcas begins to return to the Demon World through Alaindelon. While they were being transported, Baby Beel grabbed onto Lamia and refused to let go, causing Furuichi and Oga to be transported as well. All 4 of them landed in Vlad's Haunt, one of the most dangerous areas in the Demon World, with Alaindelon unconscious. Lamia manages to contact Hilda through her cellphone, and is informed that Alaindelon's daughter might be able to transport them home safely. A Yople alien shows up, which Oga punches, causing the Yople to call the creatures in Vlad's Haunt to attack the group. As the group escapes to find Alaindelon's daughter, they encounter numerous creatures, with Furuichi suffering the worst of their attacks. When the group finally reaches their destination, they realise the place was ransacked by bandits, Gare and Edda, who have kidnapped Alaindelon's daughter. As Oga defeats the bandits easily, the episode ends with Furuichi realising how attractive the daughter is.Watch Now:Amazon
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.Watch Now:Amazon
A stray cat becomes attached to Oga, causing Beelzebub to become extremely jealous and shock anyone he shows affection towards. Beelzebub challenges the cat to a fight and subsequently loses, but when a gang of fierce cats gang up on the cat for fighting in their territory, Beelzebub stands up for him, prompting Oga to help out. Afterward, Beelzebub and the cat become friends. Later, Oga takes Beelzebub and the cat to a play center where he once again meets Aoi in her park getup. While Beelzebub and Kota getting into heated competition with some other toddlers, Oga and Aoi have a conversation full of misunderstandings, both ending with explosive results. Afterward, the cat decides to leave in order to protect his fellow strays.
Takayuki tells Oga about the final member of the Tōhōshinki, Hidetora Tōjō, mainly to get him interested about ditching Beelzebub so Alaidelon will leave him alone. Wanting Oga to get beaten, Himekawa informs them that Tōjō works at the beach. Oga and Tatsumi go there the next day and get mistaken as part-timers for a yakisoba stand, later finding that Tōjō had actually been fire the previous night. As he keeps missing him, Oga asks Aoi to pass on a letter of challenge to Tōjō, whose henchmen find it before Aoi can rip it up. Oga gets held up to their meeting, arriving only finding a pile of beat up gang members, which Tōjō beat all by himself. Despite Aoi's warnings, Oga looks forward to finally meeting Tōjō.Watch Now:Amazon
Before destroying humanity, Lord En wants to experience everything in the human world. As Lord En is a huge fan of games and the like, he is drawn to the game centres and amusement parks there and is distracted from his original mission of destroying humanity. During the visit to Ishiyama Land it's found that he cries very easily over the slightest things that BabyBeel does or happens in general. He suggests going on a roller coaster, which everyone is against due to his crying, but still he demands to go on. He does eventually end up crying and creating fire once again on the roller coaster. Lord En then alerts Oga that he may be attacked by his private guards.Watch Now:Amazon
The students of Ishiyama High are ordered to do physical examinations amongst themselves. Baby Beel gets jealous of a toy which accidentally gets stuck to Oga's back, and locks himself inside of a locker to pout in protest. While trying to lure him out, the girls come into the room for their physicals, forcing Oga and Furuichi to hide under the desk while the girls strip off and start measuring. The girls leave the room without seeing them, despite a few close calls, and upon the girls' departure Oga and Furuichi get up from under the table and start trying to lure Baby Beel out once more. Aoi returns to the classroom moments after leaving, and finds the two of them in the room. She realizes that they have been there all along, and goes on the offensive. During the conflict Baby Beel exits the classroom through an open window and climbs into Sadohara's sports car, and locks the door behind him, which Oga is unable to pull open. Baby Beel "springs a leak", filling the car. Oga, unable to think of any other option, chops the car resulting in the entire shell of the car shattering.Watch Now:Amazon
Oga reflects on Lamia telling him to take a shower before going to Tojo and sees a silhouette outside his bathroom window and thinks it's Lamia, but it's really Shiroyama, who takes Oga to Kanzaki and Himekawa who tell him they want to team up to beat Tojo and Oga agrees. On the way to Ishiyama High, they are surrounded by a large group of delinquents, which Oga takes care of swiftly. Upon arriving at Ishiyama High, the rest of the school is there to confront Oga, only to have Kunieda and the Red Tails take care of them for him. Tojo sets off fireworks in order to try and cheer up Beelzebub and all the delinquents are captivated by them. Oga confronts Tojo and Tojo is willing to give Beelzebub back only to have Oga tell him that whoever Beelzebub wants to stay with is up to him. Beelzebub's fever breaks and he immediately goes to Oga and climbs on his head, and a flashback shows Oga reconnecting the bond between him and Beelzebub. Just as the episode ends, Oga and Tojo are about to begin their fight.Watch Now:Amazon
The mark on Oga's arm goes back to its small size, much to the chagrin of Hildegarde who destroys his games console. She brings a play room for Beelzebub to play in, but upon building it, it turns out to be a magical cage that both she and Oga get stuck inside. The only way to get out is to have Beelzebub solve a block puzzle toy, but he just ends up breaking it. Frustrated, Oga utilises his Zebel power to punch his way out, though it makes his mark grow big again. Rummaging through a bag of demon world toys, Beelzebub opens a chest that transforms Oga and Takayuki into nurses, which can only be reverted by helping Beelzebub play Doctor. Oga decides to use the opportunity to try and do good deeds and get rid of his mark, though has trouble handling the demonic medical supplies. After some failed attempts at treating some of the students, they change back after discovering an actually useful tool on Beelzebub's costume, but accidentally triggers an explosive that negates all the work Oga did getting his mark down to size.Watch Now:Amazon
Oga returns home after being defeated by Tojo to find that Hilda has returned from the Demon World with the imperial doctor, Forcas Rachmaninoff, and his assistant, Lamia, to help determine the cause of Beelzebub's illness. He diagnoses the illness as King Fever and when Beelzebub was trying to draw out massive amounts of demonic power, he accidentally severed the link between him and Oga and found Tojo similar to Oga and connects to him. Oga begins a treatment to try and reconnect with Beelzebub and enters a dream world through the effects of a Demon World drug that is shot into his head where he eventually finds a sleeping Beelzebub in the middle of several inscribed circles that are shrouded in an electrical field. After about 6 hours of treatment, Oga still has not waken up and Lamia assumes that he has died and becomes happy. Oga suddenly wakes up and spanks Lamia and claims he is teaching her some manners. Hilda asks Oga how he feels after having gone through the hard part of reconnecting with Beelzebub and Oga says he is in the mood to get Beelzebub back.Watch Now:Amazon
As Kanzaki tries to come up with a new special move to beat Oga, his followers suggest the key to Oga's power is having Beelzebub on his back. Thus, Kanzaki starts training with a weighted baby doll on his back. When that plan doesn't work, they try finding a living substitute, which end in more embarrassing results. Meanwhile, Oga takes Beelzebub to the park where they once again meet Aoi, who has lost track of Kouta. Kanzaki coincidentally finds him and deems him a worthy substitute for Beelzebub. Whilst playing with him, he figures out the key to performing his new special move. After returning Kouta to Aoi, Kanzaki performs his special move, though it just leaves everyone confused. As Kanzaki leaves, Oga admits his move was surprising.Watch Now:Amazon
Furuichi and Oga survey the school from the roof searching for emblems on people's shirts, and Azusa ends up tagging along in their search. Two students from St. Ishiyama are seen hassling two of Aoi's gang, causing Shiroyama to interject, telling them to leave. The two disgruntled students are offered a free punch by Shiroyama as compensation for breaking off their advance on the girls. They roll a large weight onto Shiroyama, hospitalizing him. Kanzaki bursts into the classroom the two boys are in later that day to get vengeance, only to be knocked out by Miki in one blow. Miki the invites the students of Ishiyama High to meet him on the roof after school. Himekawa, Natsume, Furuichi, Oga and Aoi all go to the roof after school, though Furuichi stays in hiding. Another member of the 6 Holy Knights is revealed, Go, from the Amateur Radio Club. The four known members of the 6 Holy Knights are all waiting on the roof when the Ishiyama High students arrive. Natsume fights Go, while Himekawa faces Sasaki, and Oga stands against Alex. Oga attacks Alex, knocking him out in one punch. Miki steps in to challenge him, claiming to know Oga from a long time ago, and to have surpassed him. Oga claims to not recognize him, but takes him seriously, passing Baby Beel onto Aoi in order to fight properly.Watch Now:Amazon
Takayuki is dragged away from his tropical summer vacation against his will to join Oga and Beelzebub to a public pool, though Oga is soon shocked by the fact he could've gone to the tropical resort himself. Whilst chatting with the Red Tails, Takayuki is approached by some delinquents from his old middle school and ends up going against their leader, Takashima, when they start hitting on the girls. Takayuki tries to hide in the pool, but Takashima calls more of his men and tricks the lifeguard into evacuating the pool, leaving Takayuki and a stunned Oga. As Takayuki becomes surrounded, he forces Beelzebub to cry in order to shock all the delinquents before facing Oga's wrath.Watch Now:Amazon
Oga attempts to explain the whole situation to Aoi, but him and Furuichi get stuck on remember BabyBeel's name. Not long after, a demon maid servent who looks similar to Hilda named Yolda appears, and expresses her unhappiness on the situation. Soon another 2 demon maid servents appear along with a young boy who is introduced by the maids as Lord En, BabyBeel's older brother, who has come due to BabyBeel taking too long to destroy humanity. Aoi then understands everyone that's going on. BabyBeel and Lord En do not have the best relationship, where BabyBeel is constantly ignoring the attention-seeking Lord En, making him upset. Lord En is also seen to love anything to do with games.Watch Now:Amazon
Finding Alaindelon's daughter rather attractive, Furuichi vows to rescue her while Gare and Edda leaded him to Oga and Lamia in the village of thieves where Alaindelon's daughter, Angelica is trapped. The rescue runs smoothly until a large Demon named Vlad's Master is awakened and terrorizes the village in which Beelzebub suddenly growed bigger and larger to fight it off.Watch Now:Amazon
The festival is underway, and Azusa is trying to run a Maid café. Furuicihi offers to help, and Azusa and her friends obey his commands blindly due to his reputation as 'The Strategist'. Furuichi persuades many of the Red Tails to dress up in Maid uniforms, claiming that this is a preliminary battle against a café that the 6 Holy Knights are running elsewhere. Hilda also gets involved, and remodels the café to be more formal. Some rowdy guests from Teimo High enter the cafe acting unruly, whom Hilda is quick to discipline.Watch Now:Amazon
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.Watch Now:Amazon
Baby Be'el is having a great time at a railroad crossing and wishes Oga to sing with him. Oga, however, is thinking about the Izuma's words about demon powers. Aoi, who is happens to be behind them, runs into Nene and Yuka, and they once again assume Aoi is going to confess to Oga. At school, Oga has become a celebrity for the "magic trick" after the volleyball match. Furichi drags Oga into creating another illusion a.k.a. making Furichi disappear by sending him flying using his mindless violence. Aoi, not convinced, confronts Izuma; however, she doesn't make any progress. Later, Tōjō talks to Shizuka stating his fight with Izuma isn't over. The two meet on the roof, and Oga joins in. However, before they can begin, Saotome beats them up and brings the unconscious Oga and Toujou to clsss. This causes confusion (as well as having a new teacher). Nene and Ryōko try to fight the new teacher for harassing Aoi. Aoi questions Saotome about Oga, resulting in more embarrassment on her part. She gets frustrated and decides to invistigate. Oga regains consciousness and leans that Tōjō ran off after coming to. Soatome appears on the roof to close the interdimensional hole created by the fight. Aoi returns to the gym and finds there proof that Oga's demon powers were no magic trick. She runs out when the hole is holes (it sent a big blast into the sky). Hilda appears on the roof to fight with Saotome because she believes him to be and agent of Behemoth. She warns him not to harm Beel. Aoi, meanwhile, manages to catch a glimpse of Hilda's demon powers is action.Watch Now:Amazon
It's revealed that Tojo and Suzuka know each other from the past, as they both underwent training from Saotome. Izumo and Tojo have a fight after school and Izumo reveals some of his demon powers. However Behemoth's 34 Pillar Divison has arrived and causes trouble. Aoi is captured by one of the pillars named Hecatos who wants to make her his contractor so that he can use all his powers in the human world. Oga and Hilda then fight together against him in order to rescue Aoi, however just before they believed they'd won Hilda is stabbed by Hecatos.Watch Now:Amazon