Noriko Sonozaki is noted for her striking beauty and ethereal presence. She has pale skin, silver eyes, and long light blue hair, which she styles with a braid along the crown of her head. Her calm and elegant appearance sets her apart from her peers, reinforcing her enigmatic role within the series.

Her outfit is a modified version of the standard Sugomori High School uniform, distinct from the other female students. It features a streamlined blazer and skirt, accented with blue detailing. Underneath, she wears a ruffled long-sleeved blouse and a ruffled petticoat, adding a refined and slightly formal touch to her ensemble. She completes her look with thigh-high white socks, black school shoes, and a pale blue bow in place of the school’s typical necktie.

Around her neck, she wears a diamond-shaped imprint, resembling a choker necklace, which conceals her Kiznaiver scar revealed for the first time at the end of Episode 8 and shown clearly throughout Episode 9. This mark identifies her as a participant in the Kiznaiver system, though it had remained hidden for much of the series.

Noriko is estimated to be around 165 cm (5’5”) tall, though her uniform shoes add approximately three additional centimeters to her height. Her appearance, both in form and attire, reflects her role as both an orchestrator and participant in the Kiznaiver experiment.

Noriko Sonozaki is characterized by her calm, emotionless, and often cold demeanor, rarely displaying outward signs of feeling. She speaks with authority and precision, especially when addressing the Kiznaivers, often delivering her words in a detached and firm tone. Her dedication to the Kiznaiver experiment appears absolute she views it as a means of achieving world peace, yet paradoxically, she struggles to connect with others on a human level herself.

Her intimidating beauty and emotional restraint parallel Katsuhira Agata, the protagonist, drawing a visual and thematic similarity between them. However, flashbacks from Katsuhira’s childhood reveal a very different Noriko one who smiled often and showed genuine warmth, suggesting that her current personality is the result of trauma and long-term emotional suppression

Noriko’s singular focus is on the success of the Kiznaiver project, which she treats as her life’s purpose. She tells Mutsumi Urushibara, her caretaker and the project’s overseer, that she will not allow the experiment to fail, regardless of the consequences. She even confronts the Mayor, speaking harshly and without hesitation when informed that the project may lose funding. Despite her authoritative tone and insider knowledge, she eventually admits that she does not fully understand the emotional intricacies of the Kiznaivers. For example, while she assigned each member a sin based on the Seven Deadly Sins, she acknowledges that none of them truly embody the traits they were labeled with, revealing her imperfect grasp of human behavior.

Beneath her cold exterior, Noriko appears to long for connection, particularly with Katsuhira. Before he became a Kiznaiver, she told him that everyone in the world wants to connect with someone, hinting at her own internal desire to be understood. Her interest in Katsuhira’s feelings becomes more evident in Episode 9, when she asks him if he likes her and how often he thinks about her, revealing a rare glimpse of personal curiosity and vulnerability.

The reason behind her emotional numbness is revealed in Episode 10: Noriko has been taking a nullifying medication for years to suppress the overwhelming pain she absorbs from the nineteen test subjects of the original Kiznaiver experiment. This treatment, while shielding her from the agony of shared pain, has also muted her own emotions, leaving her distant and unable to fully express what she feels.

Noriko was a subject in the original Kizuna Experiment as a child, during which she became permanently connected to Katsuhira Agata. As a result, she absorbed most of his physical and emotional pain. This connection deeply affected both of them—Katsuhira became numb to pain and emotion, while Noriko was burdened with the emotional weight of both herself and him.

Now serving as the public face and overseer of the renewed Kiznaiver Project, Noriko manipulates events from behind the scenes in an effort to understand and expand the potential of emotional bonds through shared pain. Her motivations are rooted in a desire to rediscover lost emotions and perhaps regain what she lost in the original experiment.

Katsuhira Agata
Noriko shares a deeply intertwined past and emotional connection with Katsuhira Agata, although he initially fails to recognize her when they reunite. Despite his confusion, Noriko demonstrates familiarity with him, remarking that he “hasn’t changed,” and displays an unusual level of physical closeness that suggests emotional familiarity. She also accepts Katsuhira’s “secret” more of a belief than an actual memory without clarification, implying she remembers something significant that he has forgotten.

As Katsuhira begins to seek connection and self-awareness, he becomes increasingly drawn to Noriko, sensing that she is tied to his recurring nightmares and flashbacks. Their bond becomes more evident in Episode 9 when Noriko removes her choker, revealing a Kiznaiver scar, and asks Katsuhira if she exists inside him. This moment confirms that she is the girl from his childhood memories, and Katsuhira embraces her in response.

Noriko expresses a desire to “find herself within him,” but notes that this can only happen when Katsuhira regains the ability to feel pain. It is revealed that they shared mutual love as children, and in the final episodes, Katsuhira openly declares his love for her. After they fall from a bridge due to her Kiznaiver reaction, the two wake up in the hospital and reconcile. Their moment is nearly romantic, but they are interrupted by their friends. Noriko jokingly tells Chidori that their relationship will start pure—unless Katsuhira eventually pushes her to the ground

Chidori Takashiro
Chidori sees Noriko as a rival for Katsuhira’s affection, harboring jealousy and frustration throughout the series. She is bothered by Katsuhira’s growing attachment to Noriko and struggles with her feelings as she watches him drift away. Although she initially denies her jealousy, it becomes evident as she grows more uncomfortable with the situation. By the final episode, Chidori accepts Katsuhira’s feelings for Noriko, recognizes her own selfishness, and helps him rescue Noriko during a critical moment.

Mutsumi Urushibara
Mutsumi is one of the researchers involved in the original Kiznaiver experiment, and she has a close, almost familial bond with Noriko. She refers to her as “Nori-chan” and has expressed that she views Noriko and the other test subjects as younger siblings. Mutsumi is highly protective of Noriko and deeply affected by the suffering she endured as a result of the experiment.

Nico Niiyama
Nico disapproves of Noriko’s manipulation of the Kiznaivers but maintains a hopeful and open-hearted attitude. Despite Noriko’s initial indifference, Nico still tries to befriend her. By the end of the series, Nico warmly invites Noriko to be a part of their group, signaling a new beginning in their relationship.

Hajime Tenga
Tenga often clashes with Noriko, frequently expressing his frustration and distrust toward her. He dislikes how she controls the Kiznaivers’ lives and how calm and aloof she remains during emotional conflicts. Noriko largely ignores his hostility, simply asking him to speak more politely. Tenga’s resentment is also fueled by his unrequited feelings for Chidori and his belief that Noriko is coming between Chidori and Katsuhira. By the end of the series, Tenga appears to have moved past his anger, even teasing Noriko and Katsuhira for being affectionate with each other.

Yoshiharu Hisomu
Hisomu treats Noriko with politeness and respect, much like he does with everyone. While their relationship isn’t explored in depth, there are no signs of hostility or conflict between them.