Shuuichi is a tall and slim young man with short, light brown, greenish hair and striking lime-green eyes. He is almost always seen wearing the standard Kitauji High School boys’ uniform, giving him a neat and composed appearance.

Shuuichi is friendly, polite, and generally easygoing. He approaches most situations with calmness and tends to take things in stride. Although quiet at times, he puts genuine effort into whatever he does and is always willing to help others when they need support. Shuuichi has a habit of picking up bits of gossip circulating around the band, though he rarely spreads them—he only shares a few with Kumiko Oumae, usually in confidence. It is implied throughout the story that he has a crush on Kumiko, and he becomes noticeably shy whenever topics related to romance arise.

Shuuichi’s story in Sound! Euphonium begins with an early encounter at a park near Kumiko’s home. The two share an awkward conversation after reuniting, and Kumiko leaves shortly afterward, telling him that she has decided not to join the Kitauji concert band—setting the stage for the gradual rebuilding of their friendship as the series unfolds.