Sound! Euphonium the Movie - Our Promise: A Brand New Day

Kumiko Ōmae enters her second year at Kitauji High School with a mix of excitement and uncertainty. The atmosphere is vibrant as new first-year students join the concert band, setting the stage for new dynamics within the group.

The concert band welcomes fresh faces, including first-year students Kanade Hisaishi, Mirei Suzuki, Satsuki Suzuki, and Motomu Tsukinaga. Kumiko and her peer, Tomoe Kabe, embrace their roles as mentors, eager to guide these newcomers toward success.

With aspirations of winning gold at the national concert band competition, the band rallies together under the leadership of president Yūko Yoshikawa. However, Kumiko quickly feels the strain of contrasting experiences between the upperclassmen and enthusiastic newcomers.

During the Sunrise Festival, tensions rise as Mirei Suzuki expresses her discontent with the perceived frivolity among senior band members. In an encouraging spirit, Kumiko and Kanade rally Mirei, helping her find renewed motivation as they prepare for their performance.

As rehearsals intensify, the band’s conductor, Noboru Taki, reveals the competition piece, 'March Sky Blue Dream.' This pivotal announcement marks a turn in the team's focus, setting them on a path towards rigorous practice and preparation.

Kumiko grapples with the dual demands of her musical commitments and personal life. She attends the prefectural festival with her boyfriend, Shūichi Tsukamoto, and discusses the challenges of their impending third year in high school with her friend Reina Kōsaka.

The band faces a setback when Tomoe Kabe announces her withdrawal from the competition. Struggling with health issues, she confides in Kumiko, leading her to reassess her commitment and position within the band.

A confrontation arises between Kanade Hisaishi and Natsuki Nakagawa during rehearsal. Kanade expresses her hesitation to participate due to a desire to let Natsuki shine, revealing the complexities of mentorship and competition within the band.

Kumiko steps in to mediate the situation, drawing on her insights from past experiences. The audition concludes in triumph, solidifying the bond among Kumiko, Kanade, and Natsuki as they face challenges together.

Under the guidance of their instructors, the Kitauji High School Concert Band embarks on a journey of growth and transformation. This evolution tests their unity and dedication as they strive for excellence.

In a mature turn of events, Kumiko and Shūichi mutually decide to part ways, choosing to prioritize their individual growth and the band's development. This decision highlights their maturity and commitment to personal ambitions.

The stakes rise as the band participates in the Kansai competition, where they are cheered on by supportive alumni. Despite their hard work and enthusiasm, they face disappointment as they do not achieve their national dreams.

After receiving a disappointing dud gold medal, the band’s leaders gather to regroup and reassess their strategies. This moment of reflection allows them to learn from their experience and plan for the future.

In the fallout of the competition, Kanade warmly welcomes Kumiko, who is now stepping into the role of the band's president. This transition marks a new chapter in Kumiko’s musical journey and signifies her growth as a leader.