Igarashi hits rock bottom as he loses his family and his job. He flees society on a ferry to Hinoshima - “Japan’s last hidden paradise.” There, he meets Tonbo, the island's only middleschooler. As Igarashi explores the remote island, he senses something odd—a pervasive golf theme, despite no golf course or known golfers on the island. What secrets does this golf-enveloped, mysterious island hold?

Tonbo decided to leave the island, which greatly impacted the residents of the surrounding islands. Amidst the mixed emotions, a farewell golf tournament was held, with just one day left until departure.

Having decided to leave Hinoshima, Tonbo boards a ferry with Igarashi, bound for Kagoshima. On the ship, the two reflect on their time living on the island. Through playing golf with "Igaiga", Tonbo's world begins to broaden. As she starts to look toward the future, the warm presence of the island's residents, who have been watching over her, stays by her side.