Wishing to become a stronger individual, Kazuya Yamamura seeks out Oga Tatsumi since he is the strongest fighter from Ishiyama High. He becomes Oga's "brother" because he wants to be a delinquent. His childhood friend is Azusa Fujisaki.
Kazuya is a former "good" student from St. Ishiyama Academy. After changing his appearances over the summer in order to appear tougher to others, he vows to become a delinquent by training under the best man of Ishiyama High, Oga Tatsumi.
Kazuya Yamamura is created by the mangaka Ryohei Tamura, and he has no information regarding what Ryohei Tamura used to create him. He first appears in Beelzebub Episode 25. His Japanese voice actor is Shintaro Asanuma.
Kazuya first appears when he is shown finding the location of the "special class" in which the Ishiyama High students are taking their classes up on the 2nd floor. He looks up to delinquents like those from Ishiyama High, and has his sights set upon Oga Tatsumi, the most powerful and dangerous fighter in the class. Later that day, Kazuya and his female friend Azusa Fujisaki follow Oga and Furuichi home from St. Ishiyama. When Oga tends to Beelzebub, Azusa comments that Oga is a good father to his child which Kazuya thinks the rumors about Oga are not true. In the process of following them, they accidentally bump into the TKKH's Toujou on the street, who asks them as to where he can find the nearest JapDonalds in the area. Kazuya freezes up in shock at just who they ran into while Azusa responds to Toujou's question by telling him where he can find one. After being in the mighty Toujou's presence, Kazuya begins to doubt if Oga really managed to beat someone as powerful as Toujou is, and the two of them resume their following of the two Ishiyama High students.
Their trail eventually leads them to the end of a dark alleyway, in which a gang of delinquents from Teimo Tech have surrounded Oga and Furuichi on both sides of the alley. As Kazuya and Azusa watch, one of the punks catches him and Azusa and threatens Oga to surrender, or the hostages will get hurt. Suddenly, TKKH's Aoi Kunieda arrives on the scene and takes them out with her umbrella. With their attention diverted, the gleeful Oga pummels the punks up before the irritated Beel finishes off the remaining thugs with his trademark electrocuting cry. Amazed by how Oga demolished everyone and confusing Beel's shocking attack as one of Oga's special moves, Kazuya thanks their saviors for saving them and gets on his knees to beg for Oga to grant him the honor of being trained by him.
The following day after getting Oga's approval, Kazuya finds himself heading over to Oga's house before school in order to meet up with his new mentor, who he has dubbed as his "bro". Much to his surprise, Oga's modest house looks like any normal house, much different from the rundown and trashed house that Kazuya had pictured in his head. He is greeted at the front door by Hildagarde. When Oga finally emerges from his house, Kazuya greets him and compliments him on having such a beautiful wife from a distant country, but both Oga and Beel try their best to shoo him away from them since they see him as a nuisance. They make their way to the local train station where they run into Furuichi. Kazuya realizes that Furuichi is Oga's tactician and praises him.
During the train ride, Oga asks Kazuya about which people are the strongest at his school. Kazuya explains about the 6 Holy Knights. At school, Oga seeks out Kazuya in the recent aftermath of both the MK5 and Shimokawa being crushed by the members of the powerful Six Holy Knights. Oga and Aoi get into trouble as Kazuya returns to find Oga and Aoi in a fight with two of the Six Holy Knights, and watches in shock as Ichiro and Oga square off against each other while Aoi deals with Sakaki. While Oga tries to test Ichiro's intelligence to see if Beel would become interested in him, Kazuya yells at Oga about Ichiro's reputation as a championed boxer. After Ichiro let Oga off, Kazuya goes to Oga's side; Miki tells Oga where they can meet.
Another event has passed when Shiroyama's beatings made Kanzaki attack a class of students, Kazuya learns that Oga, Himekawa, Natsume, and Aoi meet up with Miki, Ichiro, Sakaki, and Gou on the rooftop to settle things. He, Azusa, and Furuichi watch the battle between the 6 Holy Knights and Ishiyama delinquents in the stairwell. During the battle, Kazuya provides commentary about the members of the 6 Holy Knights to Furuichi. Suddenly, a man wearing glasses appears behind the stunned Furuichi, Kazuya, and Azusa in the stairwell, and he walks past them and onto the roof. He is none other than Izuma Kaname, the leader of the Six Holy Knights and their most powerful member. He tries to bring the fighting to a end, but that plan fails when the eager Toujou arrives on the rooftop spoiling for a good fight against the Six Holy Knights.
Being just a average human as with the majority of the minor characters in Beelzebub, Kazuya does not have any special abilities or techniques that he uses against others. He has sought training under Oga as his "sworn little brother" in order to become a stronger person.
*This only appears in the anime.
Recalling the powerful electricity attack that Oga used the other day against the Teimo Tech punks, Kazuya asks Oga to teach him that secret move during lunch. Oga reluctantly agrees to train Kazuya. After school, Oga has Kazuya doing a strange gesture and shouting "Jowa!" As he practices this new move, Beel becomes annoyed due to being hungry and bored from waiting around and eventually triggers another electrocuting wail that throughly shocks the unsuspecting Furuichi. After the training, Kazuya finds out Azusa has left with a bald man. Fearing that Teimo punks has kidnapped her, he rushes to confront the man at Aoi's temple home. However, the man is harmless as he is only asking Azusa to lead him to Aoi's grandfather to deliver a potato.