Nei Ōkawamura is an eleven-year-old girl who serves as a scout and reconnaissance specialist for the Seventh Squad of the Mato Defense Force. She is the youngest member of the unit, yet she holds the rank of a senior officer because she joined before the protagonist, Yuuki Wakura. Nei is a gentle and hardworking child who displays a level of maturity beyond her years, often acting as a voice of reason and providing emotional support to her teammates. She has long pink hair that reaches her waist, bright blue eyes, and a calm, polite demeanor. Despite her youth, she carries a strong sense of responsibility and takes her duties seriously, but she also retains an innocent and caring nature.

Her background is marked by tragedy. Both of her parents disappeared in a Mato disaster, and she was taken in by her great-aunt, Dr. Keino Ōkawamura, a leading researcher at the Mato Equipment Laboratory. The desire to find her missing parents is the driving force behind her actions. After eating a Peach, she manifested a rare clairvoyant ability called Promise (Kitto Mitsukeru), which allows her to see distant locations, detect the presence of Shuuki monsters and gate openings, and share her vision with others by touch. This power makes her an indispensable asset to the Seventh Squad, which is responsible for the southwestern region—an area with high Shuuki activity. Because her ability is purely sensory, Nei does not participate in frontline combat; she remains in the dorm as a lookout or accompanies her squad as a support element.

Within the story, Nei is a loyal and reliable member of the team. She forms a close bond with Yuuki, whom she treats as a junior despite being younger. She often looks out for him, teaches him the ropes of base life, and encourages him. Yuuki, in turn, teaches her household skills, and Nei works hard to improve her cooking and cleaning so she can help her great-aunt, who is busy with research. Their relationship grows into a warm, sibling-like dynamic. Nei also interacts well with the other squad members, including Kyouka Uzen, the commander, and her fellow soldiers Himari Azuma and Shushu Suruga, all of whom appreciate her diligence and cheerful presence.

When Kyouka temporarily lends Yuuki’s slave ability to Nei, she activates a unique form called Endless Chain: Kiraraboshi. This form enhances sensory perception, granting heightened hearing and telescopic vision, and even allows her to see through objects. However, it lacks the physical power of other forms, emphasizing her role as a scout rather than a fighter. Over the course of the series, Nei demonstrates growing confidence in her abilities and begins to rely less on her need to overcompensate for her loss. Her unwavering hope of reuniting with her parents and her quiet determination to protect those around her define her character arc, making her a grounding presence in the often chaotic world of Mato.