Ahiru no Sora follows Sora Kurumatani, a boy who has loved basketball since childhood despite being held back by his short height. Refusing to let that disadvantage define him, he pours everything into the sport and carries a stubborn determination to prove that hard work can overcome expectations. Honoring his mother's wishes, Sora enters Kuzuryuu High School hoping to build a new life around basketball and compete in tournaments, only to discover a team that has lost its way. The boys in the club are more interested in picking fights and causing trouble than playing the game, and the program itself has drifted far from the discipline and unity it needs to survive.
That begins to change when Sora meets the Hanazono brothers, Chiaki and Momoharu, two students who understand the club's disappointment and frustration from the inside. By challenging the team to a match, Sora forces everyone to confront how far they have drifted from the sport they once loved and how much they still have to prove. His skill, persistence, and relentless spirit slowly pull the group back together, rekindling their enthusiasm and giving Kuzuryuu High's basketball club a real chance to become a team again.