Kiriya is the dedicated teacher in charge of the homeroom class at Hanzō National Academy, the setting for much of the series. He is a tall, slender man with a calm and composed demeanor, which is complemented by his distinguished silver-gray wavy hair and auburn eyes. He is typically seen dressed in a formal black suit, reflecting his professional and serious nature. At forty years old, he carries himself with the experience of a former first-class ninja, and despite stepping down from active duty, his skills have not diminished with age.

Kiriya’s personality is defined by a strict and earnest approach to teaching. He is fiercely dedicated to the development of his students, pushing them through harsh training regimens daily. This rigorous attitude stems from a painful event in his past. Before instructing his current class, his first student was a promising girl named Rin. During Rin’s final graduation exam, Kiriya made the mistake of intervening to save her from a dangerous situation, helping her to pass even though she was not fully prepared. Shortly after her graduation, he received news that she had died during a mission. Believing his own softness and interference were directly responsible for her death, he vowed never to repeat that error. As a result, he refuses to coddle his students or shield them from the challenges they must overcome on their own, ensuring they are truly ready for the harsh reality of a shinobi’s life.

Despite his severe exterior, Kiriya is deeply protective and cares profoundly for his charges. His primary motivation is to provide them with the tools and training they need to succeed, hoping they will grow into fine shinobi who can survive the dangers of their world. He believes in allowing them to find their own path, even if that means going against orders. In one instance, he breaks direct commands from his superiors to unite good and evil shinobi, believing that the new generation must follow their own will.

Within the story, Kiriya serves as a mentor and source of guidance for the students of Hanzō Academy, which includes Asuka, Ikaruga, Katsuragi, Yagyū, and Hibari. His relationship with them is built on mutual respect, though he maintains a professional distance to avoid repeating past mistakes. A key relationship in his life is with his former student, Rin. It is later revealed that she did not actually die but became the severe instructor Suzune of the rival Hebijo Academy. Their eventual reunion forces Kiriya to confront his past guilt and accept that his student has forged her own path.

Throughout the series, Kiriya shows subtle development as he learns to let go of his absolute control. He eventually trusts his students to make their own decisions, culminating in him supporting their choice to ally with rival ninjas to face a greater threat. He acts as a narrative anchor, often providing historical context and missions to the younger characters.

In terms of abilities, Kiriya is an exceptionally powerful ninja from a long line of elite shinobi. Though he rarely engages in combat, he has demonstrated his prowess on the few occasions he has fought, such as destroying training dummies and armor with a single strike. He relies on his speed and experience, and even in non-combat roles, he displays skills like creating complex training dummies and using a Shinobi Barrier to create private combat spaces. In lighter, non-canon spin-off titles, he adopts the flamboyant persona of Mr. K, acting as a high-energy host for events, which contrasts sharply with his usually reserved character.