Shortly after the British exchange student Isla returns home, the Nijigasaki High School Idol Club receives an invitation to the School Idol Grand Prix, or GPX. This is a major new competition where students enter as individuals rather than as a school, using a streaming application to perform and determine who is the most promising school idol at that moment.

Eager to participate, six club members—Ayumu Uehara, Kasumi Nakasu, Shizuku Osaka, Kanata Konoe, Emma Verde, and Lanzhu Zhong—travel to one of the event's venues in Okinawa. They are welcomed by the island's gentle sunshine and abundant nature, where they join other talented school idols from across Japan, all giving their best performances. However, while the competition is exciting, Ayumu finds herself struggling with complex feelings about the prospect of directly competing against her close friends to climb the rankings.

During their time in Okinawa, the girls encounter new faces, including a girl named Ten Akamine, who is playing a sanshin in a quiet garden. It is revealed that Ten and her friend, Koito Ishimine, were once school idols themselves, but a disastrous first performance led to them growing apart. Through encouragement from Emma, Ten performs again, recalling the joy of being an idol and ultimately reconciling with Koito.

Meanwhile, a separate conflict arises when Lanzhu's mother, a successful businesswoman and a sponsor for the GPX event, arrives. Lanzhu initially believes her mother is trying to give her an unfair advantage, and considers dropping out of the competition in protest. With mediation from Kasumi, it is revealed that Lanzhu's mother's intentions were simply to improve the event's accommodations and stages in response to feedback, a misunderstanding born from a lack of clear communication. Once the conflict is resolved, Lanzhu and Ayumu are able to put on a strong joint performance.