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Description
Kyosuke Kiriya is a student at Johnan High School who appears during the second half of the series with the goal of becoming an Oni, a warrior trained to fight monstrous beings known as Makamou. He enters the story as a transfer student who quickly demonstrates talent in various areas, from playing the trumpet to shogi and drawing, which builds his confidence in his own abilities. Despite these skills, he struggles significantly with physical activities and athletic training.

Kyosuke possesses a highly ambitious and competitive personality. He prefers to solve problems his own way, even if that involves bending the rules or deceiving others, and he frequently boasts about his skills while finding excuses to avoid demonstrating them, such as faking injuries to sit out physical education classes. He can be cold and dismissive toward anyone he considers inferior, often mocking them openly. This behavior extends to his initial treatment of Asumu Adachi, another student who serves as a fellow apprentice, as he frequently belittles Asumu and questions why Hibiki would spend time with someone he views as unremarkable. However, when his confidence is shattered by injury or failure, his bravado crumbles quickly, revealing a more vulnerable side that leads him to literally cry out for his mother.

The driving force behind Kyosuke's desire to become an Oni is rooted in his relationship with his estranged father, a firefighter. Seeing his father's profession as something he needs to surpass, Kyosuke views becoming an Oni as his opportunity to prove himself greater than his father. This motivation is initially seen as selfish by Hibiki, who refuses to take him as a student, but Kyosuke persists with determination. Underneath his abrasive exterior, he possesses a kind heart and is willing to help those in need, even when he knows he lacks the strength to do so, a trait born from his desire to prove his worth.

In the story, Kyosuke becomes one of Hibiki's newest students, training alongside Asumu after Akira Amami persuades Hibiki to accept them. He forms a rivalry with Asumu, whom he constantly tries to outdo while also harshly criticizing what he perceives as a lack of focus in others, such as when Akira divides her time between Oni training and school. His strict and competitive nature makes him difficult for others to tolerate, yet he remains adamant in his pursuit of becoming an Oni. He develops a particularly close student-teacher relationship with Hibiki, though he also forms connections with other Oni such as Ibuki and Todoroki.

Throughout his training, Kyosuke undergoes gradual character development. He struggles in nearly every training session, contrasting with Asumu who takes to the training more naturally, which highlights Kyosuke's lack of natural athleticism despite his determination. A significant moment in his growth occurs when he attempts to use a Yin-Yang ring given to Asumu by Hibiki, only to ultimately decide against it, realizing that relying on power that is not his own would be wrong. This moment of self-reflection impresses Hibiki and marks a turning point where Kyosuke becomes more willing to admit his shortcomings and follow instructions properly. By the finale, which takes place a year later, he has earned the right to transform into an Oni, though his inexperience with the form leads to a quick defeat when he fights a Makamou.

As an Oni, Kyosuke transforms using a tuning fork device called the Henshin Onsa Onkaku, tapping it against a solid surface to generate vibrations that engulf his body in a fiery cyan aura. His transformed state is not a suit but rather his true demon form, which gives him an Oni face as a crest on his forehead. In this form, he gains superhuman strength, speed, durability, leaping ability, and an accelerated healing factor. He wields the Ongekibou Rekka, a pair of drumsticks that serve as his primary weapons, and his fighting style is modeled after Hibiki's own taiko style, though he lacks agility and is easily hit. His signature attack involves charging his drumsticks with power, igniting them to create torch-like weapons that can shoot fireballs. He also performs an Ongeki finisher that rapidly strikes a drum attached to a target to resonate a Sound of Purification that causes the target to explode.

In later appearances, Kyosuke continues his path as an Oni and eventually becomes a teacher to other potential Oni, demonstrating how he has matured into a more responsible man while still retaining some of his arrogant personality as a tactic to push others to improve. He struggles with living up to Hibiki's reputation and initially lies about being Hibiki himself, but ultimately accepts that he must forge his own path rather than merely imitate his teacher.