Shūichi Tsukamoto attends Kitauji High School as a classmate and childhood friend of Kumiko Oumae, though their junior high friendship became strained in their third year after he criticized her. He possesses a notably tall, slim build, short light brown-greenish hair, lime-green eyes, and wears the standard male Kitauji uniform.

Friendly, polite, and generally calm, Shūichi maintains an easygoing demeanor. He is diligent in his efforts and willing to help others. While often aware of band gossip, he typically keeps it to himself, sharing details only occasionally with Kumiko. He displays shyness regarding love and is suggested to harbor romantic feelings for her.

Originally a horn player in junior high, Shūichi switched to trombone upon entering high school after a rock-paper-scissors game win, motivated by an appreciation for jazz trombone. He favors the colors blue and green, enjoys reading manga, purchasing jazz CDs, and playing games. He dislikes tomatoes but does not mind ketchup.

Within the concert band, Shūichi observes interpersonal conflicts, such as tensions between second and third-year students that contributed to second-year dropouts, and shares these observations with Kumiko.

During Kumiko's second year, Shūichi initiates a romantic relationship with her. Their relationship faces challenges, including an awkward moment at a summer festival when Kumiko reacts negatively to his attempted kiss. Later, at a band training camp, they mutually agree to end their relationship to prioritize their commitment to the concert band and focus on their future aspirations. This coincides with Kumiko's increasing responsibilities and eventual role as band president.