Toru Takamura transfers schools to live with distant relatives during his mother's hospitalization, reuniting him with Manami Sakumoto, a relative unseen since childhood. He immediately notes her physical attractiveness, sparking an initial attraction. His arrival coincides with the emergence of Manami's alternate personality, Nami. Toru becomes the first to witness and comprehend her dual nature, discovering that verbally addressing "Nami" triggers the shift from shy Manami to assertive Nami. He strategically employs this knowledge to activate Nami's protective capabilities when Manami faces harassment or bullying.

Toru develops complex romantic feelings toward both personalities, engaging in intimate encounters with Nami while sharing emotional connections with Manami. Their relationship is complicated by the personalities' shared physical form and his familial ties to their host. He actively mediates the conflict between Manami and Nami, advocating for coexistence over elimination. By facilitating communication, he helps each recognize the other's value and necessity, contributing to their reconciliation and acceptance of shared existence.

Initially displaying opportunistic tendencies toward Manami, Toru also demonstrates protective instincts, physically intervening during her bullying incidents despite occasional ineffectiveness. His character evolves from attraction-driven motivations to genuine investment in both personalities' well-being and integration. His educational status is inconsistently presented as either high school or university student due to localization changes in the English dub that attempted to age up the characters.