Katsuhira Agata is a tall and slim teenage boy, standing at approximately 176 cm. He is characterized by his droopy grey eyes and consistently emotionless expression, which reflects his dulled emotional state resulting from the Kizna System experiments.

As a child, Katsuhira had brown hair, but following the traumatic aftermath of the Kizuna Experiment, most of his hair turned white, symbolizing both physical and psychological changes.

He is typically seen wearing his high school uniform, which consists of a white short-sleeved shirt with black accents on the cuffs and collar, along with a blue tie featuring a black cross design. His appearance and attitude often set him apart from others, emphasizing his withdrawn and disconnected nature.

Katsuhira Agata is initially portrayed as emotionally detached and indifferent, showing little reaction to either physical pain or emotional experiences. Whether in joyful or dangerous situations, he remains calm and expressionless, often appearing oblivious to the feelings of others, despite an inner desire to form meaningful connections. His inability to understand emotions, both his own and others’, makes it difficult for him to bond with people, with Chidori Takashiro being one of the few individuals he retains a personal connection to.

His emotional numbness is not innate but rather the result of trauma linked to his involvement in the Kizuna Experiment. According to Chidori’s love confession, Katsuhira was once a lively and caring boy, suggesting that his indifference developed during his grade school years, likely after the experiment.

Despite his apparent lack of emotional depth, Katsuhira does care about others. He is willing to risk his own safety for the well-being of the other Kiznaivers, as seen early in the series when he jumps off a bridge to stop Hajime Tenga from doing the same. He is often bullied at school but shows no visible reaction, both because he does not feel pain and because he rarely shows emotional responses to mistreatment.

A deeper explanation for his personality is revealed in Episode 10, where flashbacks show Katsuhira as a shy but energetic child before the experiment. After becoming permanently connected to Noriko Sonozaki through the Kizna System, most of his pain and emotional responses were transferred to her, leaving him emotionally stunted and disconnected from others.

As the series progresses, Katsuhira gradually begins to regain his former self. He shows signs of becoming more thoughtful, expressive, and socially engaged, slowly breaking free from the emotional void he had lived in. He also displays a forgiving nature, holding no grudges against those who hurt or betrayed him, including Sonozaki, Tenga, and even his past bullies.

While his inability to feel pain is considered a medical and psychological condition, it also plays a pivotal role in the story. When the Kiznaivers share pain, Katsuhira remains physically unaffected, although he still bleeds and takes damage like any normal person. It is later revealed that due to his permanent Kizna bond with Sonozaki, most of his pain is absorbed by her, explaining both his lack of suffering and his emotional numbness.

Katsuhira was part of the original Kizuna Experiment as a child, during which he was permanently connected to Noriko Sonozaki. This connection caused her to absorb the majority of his pain and emotions, resulting in his present apathetic personality. His emotional decline began in grade school, as highlighted by Chidori’s confession wishing he would return to his old self.

Despite being constantly bullied, Katsuhira shows no reaction due to his inability to feel physical pain. This condition, while technically a disability, sets him apart in the Kiznaiver group, as he is unaffected when others experience shared pain. However, his body still takes damage and bleeds when injured. Over time, it is revealed that his lack of sensation is due to the residual effects of his bond with Sonozaki.

Noriko Sonozaki
Katsuhira initially claims not to know Noriko Sonozaki, but it is later revealed that the two share a deeply intertwined past as subjects of the original Kizuna Experiment. While Katsuhira has no memory of their shared history at first, he begins to experience flashbacks and emotional reactions when around her particularly when she invades his personal space, causing his heart to race. He is the only Kiznaiver who affectionately refers to her as “Nori-chan”, a name that sparks jealousy in Chidori.

Despite her cold and mysterious demeanor, Katsuhira shows a growing interest in Noriko. He is the first to ask for her contact information and invites her to join the group at the summer training camp. His emotional breakthrough comes in Episode 6, when he candidly expresses disappointment in her actions his most sincere interaction up to that point.

Chidori Takashiro
Chidori is Katsuhira’s childhood friend, and the only person who remained close to him after his emotional change. She calls him “Kacchon”, while he simply calls her “Chidori”, showing a level of comfort between them. Chidori is protective of Katsuhira cleaning his home, making his lunch, and worrying about the bullying he endures.

Although she confessed her love for him in the past, Katsuhira’s emotional detachment prevents him from reciprocating. Nevertheless, he shows concern for her well-being and expresses gratitude for her feelings. After seeing her break down during his introduction speech, Katsuhira revises it and acknowledges that he was happy to hear she once loved him. However, he remains oblivious or indifferent to her current feelings and does not return her love romantically, though he clearly values her as someone important.

Yoshiharu Hisomu
Katsuhira first encounters Hisomu during the group’s mission to track him down. While others pursue him aggressively, Katsuhira approaches him with sympathy, recognizing that Hisomu might respond better to a one-on-one interaction. Hisomu’s eccentric and masochistic nature creates an unusual dynamic between them, with Katsuhira remaining patient and open despite Hisomu’s unsettling behavior.

Later, Hisomu expresses a particular interest in Katsuhira, even attempting to hurt him on multiple occasions, suggesting that he is intrigued by Katsuhira’s inability to feel pain. Despite these moments, there’s a sense of mutual understanding between the two, though their bond remains ambiguous.

Hajime Tenga
Tenga and Katsuhira first meet when Tenga saves him from a group of bullies. From that point on, Tenga takes on a protective role, even staying at Katsuhira’s house to watch over him. Their friendship deepens when Katsuhira jumps off a bridge to stop Tenga from doing the same, showing that he values Tenga’s life over his own safety.

Despite their camaraderie, tension arises in Episode 9 when Tenga, frustrated about not being Chidori’s love interest, physically attacks Katsuhira in front of the group. Katsuhira does not retaliate or hold a grudge, choosing instead to forgive Tenga, showing his emotional maturity and empathy even in the face of violence.

Nico Niiyama
Katsuhira and Nico share a subtle, budding friendship. Although not as emotionally involved as his connections with Chidori or Noriko, Nico shows kindness toward Katsuhira, such as giving him the green peas from her meal in Episode 4. She also expresses concern for his safety, particularly when Hisomu tries to hurt him in Episode 5. Though their interactions are brief, Nico seems to genuinely care about Katsuhira, suggesting a warm, if understated, bond.