The story begins with Igarashi, who was disqualified as a pro golfer after a certain "incident" and thus moves to Kagoshima Prefecture's Tokara Islands to step out of the limelight. On these islands known as "Japan's last unexplored wilderness," he encounters a naive girl named Tonbo.

As it turns out, these supposedly unexplored islands have a homemade golf course, where Tonbo plays every day. She demonstrates genius-level prowess, playing every kind of shot with just one golf club, a 3-iron. Igarashi is amazed at Tonbo's talent, even as he harbors doubts about her only using a 3-iron. Yet, hidden deep in Tonbo's heart lies a painful, sad past….