Cruel, cold-hearted, and vicious, Reiji Kiriya is the Viper who gives Miki the scars upon his face when they got into a confrontation back in middle school. Humiliated by Oga and left with ghastly scars upon his face, Kiriya vows revenge upon Oga, no matter what it takes.
Kiriya takes Miki's charm and steps on it. Oga jumps in to fight for Miki, but Miki insists on fighting Kiriya alone. However, Kiriya slashes Miki's left cheek with his razor-sharp nails. As he talks trash about Oga and Miki, Oga points out that Miki is holding on to Kiriya's leg. Oga then grabs Kiriya's hands and force Kiriya to claw his own face with his sharp fingernails.
Reiji Kiriya, who is created by Ryuhei Tamura, has no information regarding any inspiration used to create him. He first appears in Episode 33 of Beelzebub and makes his major appearance in Episode 36 of Beelzebub. His Japanese voice actor is Akimitsu Takase.
In the duration of the St. Ishiyama Arc, Reiji Kiriya is first introduced when the past history between Oga, Furuichi, and Miki from their days back in middle school. He is the leader of a gang of delinquents back in those days, and he becomes involved when Miki comes across where they are hanging out. After taking the charm from Miki and stepping on it, Oga decides to step in and gets involved in the situation, showing his support for Miki. Frustrated, Miki makes it known to Oga that he wants to be the one who fights Kiriya, but before he knows it, his enemy strikes. With a brutal slash, Kiriya swipes his claw-like hand at his opponent's face, the razor-sharp fingernails tearing into Miki's stunned face as the strike leaves him with two gashes on his left cheek. At this time, Oga steps forward and stops Kiriya from slashing anyone again, and by using his sheer strength, twists his hand around and uses Kiriya's own claws to gouge his shocked rival's face with. Humiliated by his defeat against Oga and by what his enemy had done to his own face, Kiriya soon moves away from the area and takes up residence in Nara, the very same area that Miki ended up moving to later that year. He vowed that he would one day return to get revenge upon Oga for both humiliating him and scarring his face.
After the match between the Six Holy Knights and St. Ishiyama High concludes, Kiriya decides to crash the party by walking into the gym and taking the microphone away from the female announcer, using it to call out Oga for what he did to him three years ago. Unknown to anyone within the building, Kiriya has brought with him a large number of Teimo Tech thugs so that they can hold the St. Ishiyama students inside of the gym hostage, thus giving himself a powerful bargaining chip to use against the Six Holy Knights and against the members from Ishiyama High. With a wrong move resulting in the hostages being beaten, this terrible ploy allowing Kiriya time to enact his long-due revenge upon Oga and in what he hopes will result in his rival being expelled for breaking the fighting clause that results in immediate expulsion from the academy. Unable to fight back against Kiriya directly without being expelled, Oga stands firm, willingly taking the strikes that the pleased Kiriya hits him with, trying his best to force Oga into fighting back against him. Sensing that victory will be his, Kiriya receives a aluminum baseball bat from one of the Teimo Tech thugs up throws down to him and prepares to launch a barrage of crushing blows upon Oga with it.
Frustrated with the situation, Miki decides to step in to help Oga and with a powerful strike, smashes his fist into Kiriya's stomach. By mere inches, Kiriya manages to bring up the baseball bat just high enough to absorb the punishing blow that Miki launches at him, resulting in the bat being twisted and useless. Miki reveals to the smug Kiriya how he too was involved in the events that occurred over three years ago, and tells Kiriya that he should fight against him as well. Interested by this reveal, Kiriya remembers who Miki is and notes how he knew about him living in Nara after those events in the past transpired. Before Miki can properly respond, he is blindsided by a punishing two-way attack from two uniformed men and sent sprawling across the gym floor, looking up to see who had attacked him. Standing before him is the four most dangerous people from Teimo Tech known only as the Shadow Group, led by the cruel Koraro Mikagami and brought along by Kiriya to help in his fight against Oga. Oga and Miki eventually team up and with set of powerful strikes, put a quick and embarrassing end to Teimo Tech's fabled Shadow Group. Blown away by just how easily the Shadow Group was humiliated in battle, Kiriya decides to lean back upon the hostage card that he maintains over the Six Holy Knights and the Ishiyama High brigade in order to get what he wants.
Unknown to him, the other five members of the Six Holy Knights and the rest of the Ishiyama High students went around and took out all of the hostage takers from Teimo Tech while he was distracted. Now without the one thing that gave him a advantage in this situation, the shell-shocked Kiriya is grabbed from behind by Oga and is finally brought face to face with the very man who scarred his face three years ago. Summoning up the powerful demonic energy that Baby Beel grants him the ability to use, Oga uses these massive powers to utterly crush the stunned Kiriya with a punishing Zebul Blast that sends Kiriya flying into the air. Upon crash landing painfully on the gym floor, the horrified Kiriya tries to play possum by pretending that he is knocked out, but Oga notices it and points out that he only "grazed him. When Oga starts counting down from three, the panicing Kiriya sits up and again comes face to face with the ruthless Oga, who transforms into a demonic beast before the horrified Kiriya, who is convinced that he has seen the Demon King. Scared completely out of his sanity by what he sees before him, the freaked out Kiriya turns tail and rushes out of the gym, falling down in his panic and shouting that the Demon King is coming for them all. That is the last time that Reiji Kiriya is seen in the Beelzebub anime (as of this point).
Unlike some of the characters in Beelzebub that have special abilities or superhuman-like attacks, Reiji Kiriya is just a average human who's brutality has earned him the name "Viper" to those who know about him. He relies mainly on his brute strength and use of force in order to achieve what he wants through battle. In his earlier years, he had long claw-like fingernails that he used to slash people with, causing the two jagged scars upon Miki's left cheek, but most likely removed them after Oga used them against him in order to gouge Kiriya's face with them.