Nao is the replica created by Sunao Aikawa when Sunao was seven years old. She is a perfect physical and mental copy of Sunao, manifesting whenever Sunao wishes for a substitute to handle tasks she finds difficult or tiring, most commonly attending school. For years Nao has lived Sunao’s life for her, going to classes, studying, making friends, and participating in club activities, while the real Sunao remains at home. In school Nao is a member of the Literature Club and counts Ritsuko Hironaka as her closest friend. Despite being a replica, Nao gradually develops her own distinct consciousness, emotions, and desires, experiencing the world with a sense of wonder that the original Sunao often lacks.

Her personality is initially defined by obedience and a desire to serve Sunao faithfully, but as she spends more time engaging with others, she becomes more curious, vulnerable, and emotionally complex. The central turning point in her life comes when Shuya Sanada joins the Literature Club after an injury forces him to quit basketball. Nao finds herself bonding with Shuya over their shared taste in books, and she falls in love with him. To help Shuya distinguish her from Sunao, she begins wearing her hair in a ponytail whenever she is the one present. This romantic attachment creates a conflict because Nao knows she exists only at Sunao’s whim and that Sunao has no interest in Shuya at all. Nao worries about her future, aware that her goals are now diverging from Sunao’s, yet she has no control over her own existence.

Motivated by her feelings for Shuya, Nao starts taking small actions that assert her independence, such as secretly saving money that Sunao does not know about, and skipping school with Shuya to spend time together. She also devises a cover story about extreme mood swings to explain Sunao’s inconsistent behavior. The story follows Nao’s journey from a passive substitute into a girl who desires her own happiness and a life separate from Sunao’s commands. A key event in her development is her death saving Shuya from an oncoming train, followed by Sunao resurrecting her as if nothing happened. This triggers an existential crisis for Nao, forcing her to confront the fact that she can be erased and re-created, and to question what it truly means to be a person.

Nao’s primary relationship is with Sunao, her creator and original, a complex bond of dependence and growing separation. Her love for Shuya Sanada is the emotional core of the story, and her friendship with Ritsuko provides grounding in everyday high school life. Her notable abilities include being a perfect replica of Sunao in appearance, knowledge, and memories, the capacity to be summoned and dismissed by Sunao’s will, and the resourcefulness to act independently when necessary. Her entire arc is a classic coming‑of‑self narrative in which a manufactured being gains a soul and learns to assert her own identity.