Nanoka Kohinata is a fifteen-year-old high school girl who moves to Tokyo to live with her father and older brother, Koshiro, because their home is closer to her new school. Because their parents divorced when she was very young, she grew up largely unaware of her brother's existence, and the two do not recognize each other when they first meet by chance. She is a bright, active, and generally typical teenager who enjoys cute things, likes boys, and spends time with her two best friends. She is sweet and naive, and she finds it easy to open up to Koshiro after they discover their sibling relationship, though she is also easily hurt when he becomes angry or brusque with her. Her friends sometimes tease her about having a brother complex, a label that holds more truth than she is willing to admit to anyone except herself. Despite her initial annoyance with Koshiro's curt demeanor, she grows increasingly attached to him. As the series progresses, Nanoka comes to terms with her romantic feelings for her brother before he does, and her development into womanhood is a central thread of the story. She plays a key role as the catalyst for Koshiro's emotional conflict, and their relationship deepens through shared vulnerability and intimate moments. Nanoka's notable qualities include her emotional openness, her ability to comfort others, and her gradual self-awareness, which ultimately leads her to accept her feelings and pursue a relationship with Koshiro despite societal taboos.