Kyo Nukui is a shut-in high-schooler with a love for music, often posting his music online under the fake name of HibikiP. One day, an anonymous sender wants to meet him at a park, to which Kyo agrees, thinking it to be a middle-aged man interested in discussing music like him. However, the anonymous sender turns out to be three elementary school girls Jūn Goto, Nozomi Momijidani, and Sora Kaneshiro, who request that he play his music with their band in an upcoming concert. They perform first for him, and despite being highly impressed with their musical skills and vintage instruments, is still unsure about his decision.

Kyo agrees to help the girls with the concert, but Masayoshi Sawatari, the head of the orphanage where they live, asks him to dissuade them.

Kyo discovers that Jūn and the others are classmates of his younger sister Kurumi, but for some reason do not get well with the other kids at school. He also finds out that his childhood friend Sakura Toriumi is also an orphan from Little Wing, and asks him to keep it a secret.

Kyo and the girls have no success at all to gather attendants to the concert, and he then decides to return to school and ask for his classmates' help, while suggesting the girls to do the same at theirs.

The concert is a success, and Kyo and the girls' next step is to gather more public to make a steady income from their gigs. By suggestion of a friend, Kyo decides to make a PV of them for advertising.

Nozomi meets her grandfather, who wants to adopt her and take her to England. Kyo and the others decide to not ask her to stay in order to not influence her decision, until Kyo's sister Kurumi gives him a piece of her mind.

Kyo is invited along the girls by his friend Yuzuha Aigae to hold a concert on a resort island, unaware of her true intentions.

Uneasy with Kyo's closeness with the girls, Yuzuha comes with several ploys aganst them, just to be exposed by Sakura. When a storm approaches the island, Yuzuha disappears and after finding her, Kyo discovers her secret.

Kiriyume reveals herself as the human stand-in for the god Kiryuu. Kyo and the girls want to help her out of her isolation. Source: crunchyroll

The band returns home, where they are met by Koume, who is keen on marrying Kyo. Every little thing makes her jealous, which makes Kyo even less available. Source: crunchyroll

Kyo turns Koume down, but she declares a band battle for his heart against Lien de Famille. But first, she needs a band. Source: crunchyroll

Jun finishes writing her song, and Kyo finishes preparing the music for Team Koume. The battle begins! Source: crunchyroll