Beelzebub IV

, generally referred to as, is an infant Demon Lord. He is first sent to the Human World by his father so that he can destroy humanity; during this mission, he becomes the adoptive son of the Human Tatsumi Oga.

Personality
Baby Beel is very easily impressed, especially by strong people since he himself is still weak and loses to other babies as well as to cats. On the other hand he is not the smartest one out there and tries to force his way through the most simple problems. It is also shown that he is afraid of insects. He often displays a fondness for things that might frighten "normal" babies, such as violence, exposed muscle tissue (on an anatomy model), heavy metal music, and demonic toys.

Baby Beel used to be a crybaby who used to cry and shock Oga all the time, but as the time goes on he gradually becomes braver to a point where he is now rarely seen crying at all. This is due to Oga's continuous teachings about what it is to be a man and a Demon Lord.

Despite having his own sense of pride and power, Baby Beel can be very shy around girls who are around his age, most notably Futaba Kanzaki and Chiyo Aiba. He tends to listen and follow the two out of apparent fear, perhaps intimidation of them. When around either of the two, he has even demonstrated embarrassment at the fact that he's always nude around them, something that generally doesn't bother him in the slightest.

Tōhōshinki Arc
Beelzebub came to the human world inside of Alaindelon. He was practically drawn to Oga Tatsumi from the beginning and is usually seen clinging to his back. Oga in turn did and still does not want to keep him around since he only causes him problems with other strong people at his school.

Oga tries to give him to Kanzaki, but later Oga beats him up for the disrespectfulness to his comrade. Next day he faces with the serious problem from Beel. Beelzebub pees up like flood with his ability and Oga cries over his fortune again. They encounter the problem with an equipment from the demon world for two hours or so.

Beelzebub and Oga head out to a department store to get the Diapers, so the pee of Beezebub would be stopped. They encounter a gang of robbers named as Orz3. Beelzebub gets attached to one of the Robbers, but Oga, feeling uncomfortable over the behaviour of robber, kicks him out. Beelzebub starts to pee again, but later Hilda takes them along to the ocean before Japan can be flooded.

Prince En Arc
When others are looking for En in online games, Beel and Tatsumi are spending time training to become stronger.

Mobichi Arc
Oga and Baby Beel meet Furuichi in the school hallways of Saint Ishiyama Academy, where they ask him to buy melon bread for them. However, they end up accompanying him to the infirmary for his cold. While on their way, Oga is suddenly punched by Furuichi which causes him to become angry; Baby Beel becomes frightened upon seeing his adoptive father's wrath. Ultimately, the two teenagers have a fight but Oga is surprisngly defeated and has his head buried in the ground below, while Baby Beel worryingly sits beside him. Oga quickly rises from the ground and asks Baby Beel where Furuichi went, though the infant cannot answer his question. The two then head back to Oga's homeroom in search for Furuichi.

Instead, they are approached by Hilda and Lamia, who later take the two to the rooftop where they explain about the tissues that Furuichi has been using since earlier in the day. As the explanations end, the group then see Furuichi in the hallways inside the building and watch from the rooftop.

While watching, Baby Beel sees Furuichi get into a fight against both Kanzaki and Himekawa. As Baby Beel watches the fight,   he begins to find entertainment in the way that Furuichi handles his situations, until he finally just laughs uncontrollably at Furuichi. However, Baby Beel's expression turns serious after Furuichi manages to defeat Tōjō with the help of a new Demon, Jabberwock. Baby Beel stays with Oga for a short time afterwards on the rooftop, listening to further explanations from Lamia about the Demonic tissues, until finally they take their leave.

Oga and Baby Beel later confront Furuichi near the river, ready for Oga and Furuichi to have their fight. Baby Beel is frightened at the battle stances that they take, specifically when Oga suddenly performs his, but then the two teenagers fight while Baby Beel observes casually from Oga's shoulder. At Behemoth's summoning, Baby Beel becomes surprised and even further after Oga starts to take a beating. Oga and Baby Beel later end up merging again after using Super Milk Time to complete the fight; once the fight ends and the transformation is over, Baby Beel falls asleep and the Human teenagers gradually collapse from exhaustion. Baby Beel is subsequently taken by Hilda while he sleeps and she carries him in her arms, but she later sets him back over Oga's shoulder, where Baby Beel subconsciously holds on to him.

However, he awakens shortly after just before a fight with the Shadow Force. Following this aftermath battle, Oga and Baby Beel assist Furuichi in building a man-size hole in the ground; however, they feel aching pain afterwards. Later, Baby Beel observes the situation with the teenagers from Oga's shoulder and makes various facial expression at what is said.

Eventually, Baby Beel accompanies Oga on their way home.

Saint Saint X'mas Arc
Baby Beel falls asleep while on Oga's bed. He gradually wakes up after Hilda comes to cradle him; afterwards, he starts feeling hungry, so Hilda takes off his pacifier. He immediately jumps from Hilda's arms when Oga throws a milk bottle towards them and nearly falls to the floor, though he is fortunately saved by Hilda. However, he accidentally kisses her, resulting in her returning to her former amnesiac self.

Return to Ishiyama High School Arc
Baby Beel drinks from a milk bottle while Oga is having breakfast with his family. It is suggested by Oga's Mother that he goes to a "trial" nursery school that has recently opened up nearby. Oga's Father supports the idea; while trying to use Baby Beel's age as a reference, he realizes that he does not know it, and evidently, neither does Oga himself. Baby Beel accompanies Oga while he learns from Hilda that Baby Beel is two years and nine months old. He continues clinging on to Oga's shoulder while he talks with Furuichi about the "trial" nursery school sometime after. After some time, the three head outside so that Oga can prove that he and Baby Beel can stay further apart from one another; as it turns out, rather than fifteen meters, they can now stay apart for at least eighteen. The excercise test ends up heavily exhausting Baby Beel.

Baby Beel later goes to the "trial" nursery school with Oga and Furuichi. Sometime after they arrive, it is announced that the children will be partaking in a dancing activity together. Oga then sets Baby Beel on the ground, telling him to make new friends with the other toddlers. Afterwards, all of the children start dancing together to a song being played on the stereo.

While everyone is dancing, another toddler named Raita slaps Baby Beel on the cheek, nearly causing him to cry. When the principal of the "trial" nursery school attempts to intervene, Baby Beel speaks out to him, apparently telling him not to get involved, as he will take care of things himself. The principal then has Baby Beel and Raita build a train set together; however, Raita continues his bullying tendencies, stealing one of the trains away from Baby Beel, even telling him to construct the railroad tracks instead. Baby Beel surprisingly shakes it all off and begins picking up some of the railroad parts. As it turns out, all he has been thinking about is making new friends in the "trial" nursery school, which is why he is being unusually cheerful.

Later in the afternoon, Oga and Baby Beel head home together, where they are confronted by Raita and his older brother, who both taunt them for their behavior at the "trial" nursery school; however, the two siblings eventually realize who Oga and Baby Beel really are. As Raita's Brother goes in to punch Oga, the child-rearing gang leader tells Baby Beel that he will show him how to make friends, and he ends up punching Raita's Brother several meters away, whom he leaves with an additional warning.

Baby Beel sleeps peacefully on the morning of the new year. Later in the day, he attends a small festival held at the Kunieda residence with Oga and Furuichi. There, they briefly pray to the Gods, albeit in a more informal manner. Afterwards, they all enjoy a small meal with Oga feeding some of his own food to Baby Beel. Oga and Furuichi eat with Aoi with whom they also inform about a strange dream that Oga had in the morning. Unable to interpret its meaning, Aoi suggests that they open some fortune cookies, though Oga's message simply reads "radish", to all of the males' confusion.

On the first day of the new semester, Baby Beel, as usual, accompanies Oga and Furuichi to the reconstructed high school. The three re-affiliate with the high school throughout the morning and meet with several of the two teenagers' classmates. Natsume and Himekawa eventually explain to the three about how there is a group of first-years who are trying to reign over the entire high school, which will include taking down Oga personally.

One of them, Nasu, has already introduced himself to Oga, which later results in the child-rearing gang leader seeking him out. He and Baby Beel find him in the hallways near Kanzaki's gang. Baby Beel draws whisker-like features on Nasu's face with a marker when he comes close to the duo. Subsequently, per Oga's suggestion, the new first-year punches Oga and sends him flying into the ceiling, effectively burying his head, as well as Baby Beel's, into the concrete.

Baby Beel manages to poke his head out. He rubs his face and then starts shouting at Nasu, only to be shot a dark smile at the latter, frightening the young Demon. Moments after, Oga frees both of them from the ceiling, and he lands on the ground while holding Baby Beel's leg. Baby Beel later returns to his spot near Oga's shoulder and watches as the following events unfold. Shortly afterwards, several of Nasu's allies arrive to take him away, and he leaves with them, but not before warning Oga that he will take Baby Beel away from him.

With Nasu's leave, Baby Beel suddenly starts pulling on Oga's hair out of frustration, which Furuichi suspects is because of the stress and tension that he has been feeling earlier, something originally noted by Oga himself. Baby Beel eventually stops after two other delinquents, Ebian Ichikawa and Kankurō Akahoshi, give their warnings to Oga before leaving the vicinity.

Baby Beel later returns to the Kunieda residence with Oga and Furuichi during the afternoon. There, he gets into another childish fight with Kōta, until he later "attends" a meeting for most of the original Ishiyama delinquents. After the delinquents discuss and conclude on a set plan, they consider who is to be their alliance's leader, until they play a game of rock-paper-scissors to determine who. In the end, due to Baby Beel's participation, he is unanimously made the official "boss".

The following day, Baby Beel and Oga intrude into a classroom occupied by the Poltergeists, Kanzaki, and Furuichi.

It is then revealed that a tattoo resembling the Zebul Spell has appeared on Kanzaki's back bearing the number 1. Hilda, who is also present in the room, explains that it is the King's Crest, which signifies that a lifelong allegiance has been made between Kanzaki to Oga and Baby Beel; Baby Beel displays happiness and confidence at this reveal.

The comical atmosphere quickly tenses as Kanzaki engages in another brief fight with Taizō Shioiri, whom he easily defeats; after a brief speech directed towards Oga, Oga and Baby Beel then confront Nasu in another part of the classroom. There, Nasu reveals that he is a Spell Master shortly before a fight ensues between the two teenagers. Throughout the fight, Baby Beel continues to cling onto Oga's back, making various facial expressions at the events that occur. When Nasu eventually succeeds in overpowering Oga, he asks that Oga give him Baby Beel, then stating that he will use the infant's power entirely until it is all gone; Baby Beel momentarily becomes worried and frightened at his words. Baby Beel remains silent though alert of what is occurring around him. Fortunately, Oga is soon able to fight again, leaving Baby Beel to again oversee the fight as it goes. At the climax of the fight, Oga and Baby Beel end up merging bodies again with Super Milk Time and succeed in defeating Nasu.

After some time, they eventually separate from their merged self, though they end up switching bodies again due to Oga's forgetfulness. When Baby Beel realizes this, he becomes excited and eagerly dashes from the room, running down the school hallways gleefully in Oga's body.

He eventually stops near a female teenager standing near a window. She recognizes him as Oga and begins to strip down, asking Baby Beel to spend time for her. However, upon noticing a trio of boys nearby, she then asks that they go elsewhere. Baby Beel happily agrees to her request without a second thought. He is taken to a broken-down and desolate area, where he ends up being beaten and gagged. Baby Beel starts crying although he is quickly silenced by the woman after she makes a seductive gesture towards him. The woman then proceeds to remove Oga's upper clothing and collar his neck, moreover attaching a thin rope to the collar, which another woman named Mizuki uses as a sort of leash.

Baby Beel is later brought to Aoi and Oga while still gagged and restrained, forced to watch the following events proceed; he later ends up receiving a scolding from Oga for not manning up despite his situation. During Aoi's fight wih the woman, revealed to be Ringo Hōjō, the latter takes hold of Baby Beel and threatens to burn out an eyeball, which she then does a second time. However, sometime before the second attempt, the side effects of Super Milk Time wear off, resulting in Oga and Baby Beel being able to return to their original bodies. Oga goes to pick up Baby Beel shortly afterwards.

Sometime later, on a snowy day, Oga and Baby Beel play a card game revolved around the King's Crest and the Ishiyama delinquents. The two play a serious match against one another and it eventually results in a major disadvantage on Baby Beel's part, much to his shock. The two then notice that several of Oga's classmates have arrived though they continue to play the game, even offering the others to join in on them; they briefly stop once they see that the others care little for it, although they end up picking up their cards and resuming the game after a short amount of time.

During the next few days, Baby Beel continues to cling on to Oga's back as he does other activities with his classmates, such as play tennis.

One night, after Oga learns that Furuichi has apparently gone missing, he heads to the Ishiyama campus with Baby Beel. While strolling around, they are approached by Zenjūrō Saotome, who reveals that he formerly taught Takamiya and Fuji about Spells. Saotome elaborates more on Takamiya's situation and how fighting him with his Demon Lucifer using Baby Beel can cause a war; additionally, he claims that Takamiya is on a much higher level than Oga. However, Oga rebuffs Saotome's warnings and leaves with Baby Beel to confront Takamiya inside the school.

Oga and Baby Beel later approach the first-year in a hallway with a defeated Furuichi and other beaten members of Behemoth's 34 Pillar Division. Baby Beel observes Oga's fight with Takamiya while still clinging onto his back; following a successful Zebul Emblem, Baby Beel salutes to his adoptive father as an indication of victory but is told not to celebrate just yet. Sure enough, Oga is then abruptly hit with an uppercut that forces even Baby Beel off of his back. As Baby Beel lies on the ground, he later watches in horror as Furuichi is seemingly killed after his heart has been carved out from his body. He then looks on as the heart is then sliced into six pieces and sent throughout the campus. Enraged, Oga takes one of the pieces and then goes to pick up Baby Beel. Baby Beel goes back to clinging to Oga's back as the delinquents resume their fight.

Just when the fight appears to be hitting its end, Tōjō arrives and puts a halt to it. Baby Beel simply watches on as the following events proceed between Tōjō and Takamiya, then when Furuichi is taken away to be given treatment for his wounds.

Afterwards, Oga and Baby Beel resume the fight with Takamiya and Lucifer. Baby Beel simply clings further to Oga's back while observing the situation and allowing his adoptive father to use his powers, doing nothing else in the meantime. Eventually, Oga and Baby Beel are forced to take their fight to the rooftop of the building that they are in.

Electrocution
When Baby Be'el is caused to cry for one of various reasons, for example Oga being in danger, it fries everything in a certain range depending on how loud he cries. Generally the energy used is higher than that of a 12.000 Volt stun baton Himekawa of the Touhoushinki uses against Oga in chapter 9. Initially, if Beelzebub was more than 15 meters away from Oga, the electric shock would reach a fatal level (for Oga). Due to their new-found trust, this distance has increased by 3 meters. Recently, Be'el has shown the ability to control his lightning and shoot it with enough power to defeat an ordinary demon

Pee


Once a year Baby Be'el relieves the blessed urine that contains holy demon power. It can't be stopped by simple means such as knotting or diapers and would be able to sink a whole town. This, however was prevented by Oga and Hilda riding on Ak'Baba to the ocean.

Giant Form


In the Demon World, Beel was able to turn into a giant and easily defeat the monster of the land.

Hidden Potential
While training with Saotome Zenjuro, a radio was used that made a "shadow" of Be'el. This shadow supposedly embodies the potential of its subject, and, as it was able to easily strike Oga into a boulder and crush that boulder, Be'el is hinted to have a large amount of fighting potential.

Later, when Be'el and Oga switch bodies, Oga is seen defeating numerous delinquents using Be'el's body, implying that Be'el already has great fighting prowess but doesn't know how to control his strength.

Super Milk Time


It is revealed by Oga that he is not the only one getting stronger and that Be'el also receives a large power boost when they use Super Milk Time and they also fused after using the "Super Milk Time". At 30 CC, he was able to block the axe of Basilisk, one of the Pillar Heads, and at 80 CC, he was able to shatter the axe. Super Milk Time is a time limited technique.

Super Croquette Time
In the anime, Oga can use Baby Beel's power in turn after Baby Beel eat Croquettes. In reverse, Oga drinks Baby Beel's favorite Demon Milk while Baby Beel eat Croquettes. In this form, Oga synchronize with Baby Beel and took control of his power. He can beat Jabberwock's dragon Sodom without even failing. Oga can use a giant Zebul Emblem to destroy half of Akumano Academy building.

Ankokubutō


Ankokubutō is a technique that allows possession of the body. It is speeding up Be'el's maturation process, as he has his urination period 6 months too early. It also causes him to start teething early. This process might lead to complications later on.

Tatsumi Oga
Oga is Beelzebub's chosen adoptive father, selected both by Alaindelon and Beelzebub himself. Though they get off to a somewhat rocky start, even Hilda is surprised by the strong bond that rapidly develops between Oga and Beelzebub. When not crying or otherwise upset, Beelzebub actually listens to Oga and recalls his lessons on being a man clearly. Likewise, Oga picks up Beelzebub's speech patterns quickly and gets much better at taking care of him. Oga initially only wants to find a stronger parent for Beelzebub in order to get rid of him, but as they grow closer, this search is implied to be more for Beelzebub's own well-being than anything else: he needs a strong, qualified parent to draw out his full demon potential. But Oga already accepted him as his son. Throughout the series, Beelzebub is extremely attached to Oga, prioritizing being with over almost all else.

Hilda
Hilda has been chosen to act as the mother of Beelzebub, and raise him in the human world along with Oga. Beelzebub is close with his wet nurse, Hilda, as shown when she was stabbed by Hecadoth, he cried and even though Oga told him not to cry because Hilda is still watching them, he was still on the verge of crying. He also refused to run away when Hilda told them to run away. Also at the first series, Hilda asked if she should come with Oga to school, Oga refused. That caused Beel to cry and electrify Oga for not letting Hilda come with them. Despite Beelzebub seeming to prefer being with others at times (his refusal to leave Oga for her at the beginning of the series as well as her favoring Aoi while having a switched body) he still cares for her very deeply. He readily calls Hilda his mother, and values her happiness very much.

Aoi Kunieda
Beelzebub is very attracted to Kunieda. When Kunieda displays her strength, Beelzebub was happy. He also seems to be comfortable with Kunieda. When Kunieda was holding him during Oga's fight with Shinjo, he fell asleep in her arms, or when Beelzebub in Oga's body, he smelled demon aura from Kunieda and grasped her twice. Kunieda is also one of the few people capable to hold Beelzebub without him crying. One being Oga, and the other being Hilda. Since Beelzebub is also quite attached to Aoi, Hilda tends to be quite jealous of her.

Trivia

 * In Animax broadcasts, Baby Beel and black baby beel wears diapers over their genitals.
 * Aoi is the only person Baby Beel hasn't shocked whenever he is crying.
 * Baby Beel is currently 2 years and 9 months old