"Sound! Euphonium" centers on Kitauji High School's concert band, which has seen better days. Once a nationally competitive ensemble, the band now struggles to regain its former glory. The narrative begins with Kumiko Oumae, a first-year student and euphonium player, who joins the band with a mix of reluctance and curiosity. Having experienced the pressures of competitive band culture in middle school, Kumiko initially approaches the group with a sense of detachment.

The band’s dynamics shift when a new advisor, Noboru Taki, is appointed. Taki, a strict yet passionate conductor, challenges the students to aim for the national competition, setting high expectations for their performance. His arrival sparks a renewed sense of purpose among the members, but also exposes underlying tensions. The story delves into the interpersonal relationships within the band, particularly between Kumiko and her peers, including her childhood friend Shuuichi Tsukamoto, the driven and talented trumpet player Reina Kousaka, and the diligent but insecure bassist Hazuki Katou.

As the band prepares for the regional competition, internal conflicts arise over seating auditions, which determine who will play in the competition. The pressure to excel strains friendships and highlights the competitive nature of the group. Kumiko, initially indifferent, gradually becomes more invested in the band’s success, forming a close bond with Reina, whose unwavering dedication to music inspires her. The series explores themes of ambition, self-discovery, and the emotional weight of artistic expression, as the characters navigate their personal struggles while striving for collective excellence.

The narrative also examines the challenges of leadership through the perspective of the band’s president, Haruka Ogasawara, and vice president, Asuka Tanaka. Their contrasting approaches to managing the group reflect the broader tensions between tradition and innovation, as well as the difficulty of balancing individual aspirations with the needs of the ensemble. The story’s emotional core lies in the characters’ growth, both as musicians and individuals, as they confront their insecurities, reconcile past disappointments, and learn to trust one another.

"Sound! Euphonium" portrays the concert band experience with a focus on authenticity, capturing the intensity of rehearsals, the thrill of performances, and the camaraderie that develops among the members. The series balances its exploration of musical ambition with a nuanced depiction of teenage life, offering a compelling look at the intersection of art, friendship, and personal growth.