Natsumi Hirakawa is a short, sporty, and athletic girl who is a classmate in the fifth grade class 5-2. She possesses outstanding physical abilities and can beat anyone at sports, making her a hero among the girls and a frequent rival for the boys, particularly Ryota Sato, whom she regularly defeats in challenges. Natsumi generally does not have strong desires, but when she finds a goal, she pursues it with single‑minded focus. Despite her calm demeanor, she has nyctophobia, a fear of the dark. She is notably innocent and lacks a sense of modesty, often needing to be stopped by her friends from undressing in public in front of boys. Natsumi is a tomboy who uses the masculine first‑person pronoun boku and dresses in boys’ clothing for most of the story, though she wears a more feminine outfit in the epilogue. Her number on the class list is 17. Her key relationships include her close female friends who often have to remind her of social boundaries, and her competitive dynamic with Ryota. Over the course of the series, Natsumi’s athleticism remains her defining trait, and her only notable development is the brief adoption of a feminine appearance at the end. Her motivations are simple: she enjoys sports and is content to go along with the daily events of school life, occasionally stepping in when her focus is captured by a specific objective.