Now that Kumiko Oumae has enrolled in Kitauji High School, she hopes to forget about her past. Despite her desire for a fresh start, she gets dragged into the school's band club by her new friends—Sapphire Kawashima and Hazuki Katou—and is once again stuck playing the euphonium. As the band currently stands, they won't be able to participate in the local festival, Sunfest, let alone compete at a national level. The band's new advisor, Noboru Taki, gives them a choice: they can relax and have fun, or practice hard and attempt to get into nationals. Not wanting to repeat her mistakes from middle school, Kumiko is doubtful as to whether they should try for nationals. Amidst the chaos, she learns that her old bandmate, Reina Kousaka (who she had a bitter relationship with) has joined Kitauji's band club. Under the pressure of Noboru's strict training, Kumiko and her bandmates must learn to overcome their struggles and find success together.

Following their success in the qualifying round for the Kansai regional competition, the members of the Kitauji High School concert band set their sights on the next upcoming performance. Utilizing their summer break to the utmost, the band participates in a camp where they are instructed by their band advisor Noboru Taki and his friends who make their living as professional musicians. Kumiko Oumae and her friends remain determined to attain gold at the Kansai competition, but trouble arises when a student who once quit the band shows interest in rejoining and sparks unpleasant memories for the second-year members. Kumiko also learns about her teacher's surprising past and the motivation behind his desire to lead the band to victory. Reaching nationals will require hard work, and the adamant conviction in each student's commitment to the band will be put to the test.

With the ensemble contest behind them, the members of the Kitauji High School concert band now aim to win a gold medal at the national competition. For third-year club president Kumiko Oumae and her friends, it is their last chance before graduation. Filled with anticipation and anxiety, Kumiko worries if she can successfully lead the band. Amid her struggles, Kumiko encounters transfer student Mayu Kuroe. From her gentle demeanor to her talented euphonium skills, Mayu was a member of the Seira Girls' School concert band—a regular at nationals. While Mayu is friendly, Kumiko cannot help but have an indescribable feeling from their meeting. As new members arrive and plans are set in motion, the club, with an insatiable hunger for a gold medal, learns what it truly takes to propel themselves to reach the national level.