Kōta Kunieda

is Aoi Kunieda's younger brother. Kōta is the reason Aoi created her alter ego, Aoi Kunie, so that nobody sees her taking care of a baby, however the mothers at the park recognize her and believe Kōta is her child. He is often comically presented as Beel's rival, constantly outdoing the future demon lord in anything he attempts, which usually results in Beel crying and shocking Oga, who is usually unaware of what has transpired.

Appearance
Kota is a baby and is the same size as beezlebub. He is sometimes shown on his sisters back. Kota is shown waering a long sleeve blue shirt with the number 5 in the center. He also has on long blue pants. On top of his head is a bear hat, and on his feet are brown shoes with white bottoms. Kota shares a little similar look to aoi except he has black hair and big black eyes unlike beelzebub who's eyes are tiny.

Personality
Kouta is shown at the start to be a regular baby, but shows pleasure in tormenting baby beelzebub. Later on Kouta seems to have both a rivalry and close friendship with beelzebub. Kouta seems to care for his new friendship with beelzebub like watching hero shows together with him, and standing up together to fight off bullies.

Tōhōshinki Arc
He is first seen while he is taken to the park by his older sister, Kunieda Aoi, where many mothers at the park mistakenly believes that Aoi is his mother. While at the park he has his first encounter with Beelzebub, where he begins to wrestle with him on a park bench when Oga decides that they should have a baby fight. Kota easily wins the wrestling match by pushing Beelzebub off of the park bench, which causes Beelzebub to nearly cry.

He is next seen with his older sister, Kunieda Aoi, when they go visit their grandfather. While on the trip to see his grandfather, he is seen carried on the back by Kunieda Aoi.

Saint Ishiyama Academy Arc
He is seen again when Oga goes to Aoi's home which is a shrine, so that Oga can train properly for his fight with demons. Throughout the training sessions, Kouta is shown training alongside Beelzebub. Kouta makes Beelzebub continously cry during the training sessions because he continously outdoes Beelzebub with a tormenting smile.

Hero Show Arc
Kouta goes to a Hero Show with Beelzebub. It is here where Kouta first meets up with Kanzaki Futaba and is shown to develop his first crush on her. Kouta and Beelzebub enjoys the Hero Show and when the show ends, he and Beelzebub tries to act out some of the characters moves. At the end of the arc, Kouta is being bullied by other children and almost cries before being comforted by Beelzebub. Kouta gains courage and stands up together with Beelzebub against the bullying children, before the bullying children are scared away by their elder sister. Kouta and Beelzebub seems to congratulate each other, for believing that it was their efforts that scared away the bullying children.

Merry Christmas Arc
Kōta goes with his older sister Aoi to the shopping district in the city, where they run errands for the family. While in one of the malls, Kōta sees a selection of costume items relating to Gohan-kun and stares at them intently. Eventually, the two siblings meet with Oga and Hilda at the mall. Hilda eventually buys ice cream for Kōta and Baby Beel, even handing out Kōta's own ice cream cone to him. Afterwards, Oga and Hilda take their leave. While they leave, Kōta feels an enraged aura coming from Aoi and becomes frightened by it.

Return to Ishiyama High School Arc
When Baby Beel is at the Kunieda residence, he and Kōta end up fighting each other, though Oga tries pulling them apart so neither can actually get injured.

Aoi Kunieda
Aoi clearly loves her baby brother, as she uses her alter ego in order to distance him from her more well-known identity as the leader of Red Tail, which could potentially make him a target for her enemies. She is usually the one seen taking care of Kōta, and is the relative that Kōta responds most favorably toward so far.

Beelzebub IV
Though they are rivals who are constantly trying to outdo each other, they are still friendly at times, as neither appears to have any other friends their age.

Hajime Kanzaki
In the anime filler Kouta rolling down the hill gave Kanzaki the idea how to perform his Double heel smash.

Koma
In the Anime Kouta and Beel tried helping Koma in getting Aoi to eat his manju (filler).

Futaba Kanzaki
In the manga, Kouta develops a crush with Futaba.

Trivia

 * In the Beelzebub anime, several filler episodes are often between plot developements. In one such, Kota is shown alone at a day care playing by himself, because the other boys do not want to play him, When Beel comes along with the cat to play with him, he is happy to see them, both of them eventually beat the other babies in a game of who could stack the highest blocks by causing an explosion.
 * The anime presents the two regularly as friends as well as rivals, while the in the manga they are depicted as only as rivals. After their training at the Mapputatsu peak Beel has not been shown with Kota up until now.