Season 1

Sound! Euphonium erzählt die Geschichte des Musik-Clubs der Kitauji-Oberschule. Nach einem Lehrerwechsel ist der einstmals angesehen Club stark abgefallen, doch ein neuer Lehrer soll den Laden wieder in Schuss bringen. Kumiko Oumae und ihre Klassenkameradinnen Hazuki und Sapphire, die alle neu an der Schule sind, statten der Blechbläserband einen Besuch ab. Kumiko beschließt, dem Club beizutreten und Euphonium zu spielen, bis sie Reina sieht, ihre Klassenkameradin aus der Mittelschule. Als sie sich an einen Vorfall von damals erinnert, zögert sie.

After swearing off music due to an incident at the middle school regional concert band competition, euphonist Kumiko Oumae enters high school hoping for a fresh start. As fate would have it, she ends up being surrounded by people with an interest in the high school brass band. Kumiko finds the motivation she needs to make music once more with the help of her bandmates, some of whom are new like novice tubist Hazuki Katou; veteran contrabassist Sapphire Kawashima; and band vice president and fellow euphonist Asuka Tanaka. Others are old friends, like Kumiko's childhood friend and hornist-turned-trombonist Shuuichi Tsukamoto, and trumpeter and bandmate from middle school, Reina Kousaka. However, in the band itself, chaos reigns supreme. Despite their intention to qualify for the national band competition, as they currently are, just competing in the local festival will be a challenge—unless the new band advisor Noboru Taki does something about it.