Haibara's Teenage New Game+

September arrived, and with summer vacation over, everyday life returned. Natsuki is invited by Serika to form a band together. Confused by the sudden offer, Natsuki initially tries to refuse, but realizing Serika's enthusiasm and her own desire to live a youth without regrets, she decides to join the band. The two immediately begin searching for other band members... Meanwhile, Hikari has made up her mind to confront her feelings for Natsuki.

With all the band members finally assembled, Natsuki and the others begin practicing in earnest. For their first song to perform at the school festival, they decide to jam to a song written and composed by Serika. During the performance, Natsuki feels the stark difference in skill between herself and the other members and loses confidence. However, Serika encourages her, saying she likes Natsuki's singing voice. A week after the band was formed, Serika, struggling to write lyrics for their second song, which is themed around "the past" and "regret," asks Natsuki to write the lyrics for her.

The day of the school festival has finally arrived. Natsuki is moved to tears when she receives a class T-shirt, something that wasn't provided before her time leap. Meanwhile, Shi invites Natsuki to tour the festival with her, saying she has something important to tell her. On the second day, it's finally Natsuki's band's turn to perform on the outdoor stage. Serika, Iwano, Naru, and Natsuki nod in agreement, determined to give the best performance possible, and the curtain rises on this "ragtag group of leftovers." Where will Natsuki's feelings lead her as she sings from this prime seat of youth?