Mirei Suzuki enters Kitauji High School as a first-year student and joins the concert band to play tuba. She possesses a quiet, reserved nature, initially struggling to connect with fellow band members and often appearing unapproachable or aloof. Her serious approach to musical performance clashes with the more relaxed attitudes of some upperclassmen. This contrast prompts her temporary departure from the band during the Sunrise Festival, driven by her perception that others lacked commitment and her desire for a meaningful, dedicated band experience. Second-year student and freshman advisor Kumiko Oumae intervenes, persuading Mirei to return by emphasizing the band's collective effort and goals. Following this, Mirei reconciles with the group and gradually integrates into the bass section. Her development includes forming connections, notably with fellow tuba player Satsuki Suzuki (no relation), who actively seeks her friendship. Mirei also shares similarities with Motomu Tsukinaga, another first-year contrabass player facing social integration challenges, though their dynamic receives less focus. Her arc concludes with her remaining a committed band member, contributing to their competition preparations despite Kitauji ultimately not advancing to the nationals.