Hoshiai no Sora follows the boys' soft tennis club as it struggles to survive at a middle school where the girls' team consistently outperforms them and disbandment looms over a roster with poor skills and few positive results in matches. Touma Shinjou is determined to recruit capable players, but his search goes nowhere until Maki Katsuragi, a new transfer student, catches a stray cat in his classroom with remarkable reflexes and immediately grabs Touma's attention. Touma asks Maki to join the boys' team, only to be turned down because Maki has no interest in clubs.
Touma refuses to back off and eventually persuades Maki to join under an unusual deal: Touma will pay him for his participation and cover the club's other expenses. Once Maki is on the team, his natural talent and rapid learning quickly set him apart from the others, creating friction among the boys even as he becomes the standard they must reach.
As the club members try to keep pace with Maki and discover their own abilities, they are forced to face personal hardships and the darker side of growing up in middle school. Through their struggles, Hoshiai no Sora turns a threatened club into a story about rivalry, persistence, and the pressure of adolescence.