Subaru Hasegawa, a high school freshman and promising basketball talent, faces devastation when his school's team is suspended for a year after the captain's scandal involving an elementary schoolgirl. Contemplating quitting basketball, he is coerced by his aunt—Mihoshi Takamura, an advisor at Keishin Academy—into coaching their struggling elementary girls' team. She blackmails him using embarrassing childhood secrets, securing his reluctant agreement for just three days. After witnessing the team's imminent disbandment and the dedication of player Tomoka Minato, Subaru commits long-term.
Physically, he has brown hair and eyes, stands 172 cm tall, and possesses a moderately muscular build with a somewhat "girlish" appearance. Initially passive and indecisive post-suspension, he evolves into a determined mentor through his coaching, though he occasionally struggles with vulnerability when defending his methods.
As a player, Subaru’s skill defies his height: he once led a weak middle school team to a prefectural final. His coaching transforms the Keishin girls into contenders capable of defeating their championship-winning boys' team and rivaling elite squads like Suzuridani Academy.
Nicknamed "Subarun" and "Onii-chan," he maintains brotherly or mentor bonds with most players. The core narrative across light novels, anime, and manga subtly implies deeper romantic feelings toward Tomoka Minato ("Tomoka's Route"), contrasting with visual novels offering alternate romantic paths.
Key conflicts include overcoming reluctance, defying skepticism from rivals like boys' captain Natsuhi Takenaka, and managing interference from childhood friend Aoi Ogiyama—who transitions from critic to assistant coach. His growth culminates in the declaration, "Elementary schoolgirls are definitely the best!!" reflecting renewed commitment.
Beyond basketball, Subaru is an average student with gaming as his primary hobby. He uses the informal "Ore" and receives family support, notably from his mother Nayu, who observes his recovery from despair through coaching.