The Kitauji Concert Band Schism is a major event that occurs within the Kitauji Band in the year prior to the beginning of the first Sound! Euphonium light novel. During the schism, nearly all of the first-years whom held significantly different goals and opinions from the rest of the upperclassmen quit the band, triggering a subsequent mass desertion. This led to a huge number of members dropping out during the schism.
The group of first years that initiated the mass desertion was led by flutist Nozomi Kasaki, the former band president from her middle school's concert band.
A year before the schism, the concert band of Nozomi's middle school, Minami Junior High School, did not make the cut at the qualifying round of the All-Japan Band Competition, which created a lingering disappointment on Nozomi's part as well as the members of the ensemble whom went on to attend Kitauji High School. These students, along with Nozomi, saw their transition to high school band as a new opportunity to prove themselves at a higher level of band competition.
Nozomi and her first-year peers quickly discovered that Kitauji's concert band was at the time mired within a culture of laziness and mediocrity, where participation and seniority were valued over achievement and talent. This attitude was encouraged by the director at the time, Rikako-sensei, as well as the seniors and section leaders.
The first-years quickly grew extremely frustrated with both the ensemble and with Rikako-sensei, while the majority of the third-years wanted to maintain the prioritizing of seniority over merit. Acting in self-interest, most of the oldest students in the band who were in positions of power due to the seniority system opposed the efforts of the first-years to create a more goal-driven ensemble environment. However, many second-years in the band at the time became sympathetic to the newcomers' passionate cause to reach nationals.
When the disagreement between the first-years and third-years broke out into open hostility, the second-years at the time split into two sides. Most of them came out in favor of either the freshmen or the seniors. Some, like Asuka Tanaka, did not care about the drama and continued to focus on playing music. Others, such as Haruka Ogasawara and Aoi Saitou, tried to mitigate the conflict without taking sides. These students did their best to resolve the situation when Nozomi and her cohorts threatened to quit. Despite their efforts, Nozomi and her followers eventually chose to leave the ensemble as a final statement, and many other talented students in the band began to quit as well. Nearly half the band had deserted by the end of the school year.
Some of the members who quit joined the K-ON (light music) club in order to continue pursuing music.
Many of the members currently in the ensemble are still emotionally affected by the events of the schism. Mizore Yoroizuka, Nozomi's former best friend, was deeply hurt by Nozomi's actions, and there is now a major rift between the two students. In addition, Haruka continues to battle feelings of insecurity over her inability to prevent the schism from happening. Aoi's decision to quit the band also partially stems from her disappointment with her own perceived failure to prevent the schism.
There is also a general consensus within the ensemble that even with all the progress they achieved under Noboru Taki's tutelage, they would have been much more competitive had the first years stayed, since the members who left consisted of the best and brightest musicians of their year.
When Nozomi tries to rejoin the band in the second season, Asuka makes every attempt to stop her, out of fear that Nozomi's presence will negatively impact Mizore's emotional state and thus her musical performance. Because Mizore is a keystone player in the band's success, Asuka does not want Nozomi's presence to jeopardize the band's newfound claim to nationals. Yet eventually, Nozomi and Mizore get together again, allowing Nozomi to rejoin.
- Nozomi Kasaki- spearheaded the branch of the schism that elected to leave.
- Rikako-sensei- encouraged the culture of mediocrity that Nozomi and the first years strongly opposed.
- Haruka Ogasawara- tried to prevent the schism.
- Aoi Saitou- tried to prevent the schism.
- Mizore Yoroizuka- remains severely affected by her broken friendship with Nozomi