This article contains minor plot spoilers from the light novels that have not been revealed in the anime. Proceed at your own risk.
Shuuichi is a very tall and slim young man who has short, light brown greenish hair and lime-green eyes. He is usually seen with a standard Kitauji High School uniform for boys.
Shuuichi is a friendly young man, whom is most of the time polite. He is calm and takes everything quite nicely. He also tries his best in everything, and will help anyone in need. He is prone to picking up gossip from around the band, but does not spread them, only sharing them with Kumiko. He is presumed to have a crush on Kumiko and seems to be quite shy when talking about the topic of love.
Shuuichi and Kumiko are childhood friends, and the two went to the same junior high school. He and Kumiko are not classmates in high school however, consequently of their different choices in study courses. The pair had a falling out, due to Shuuichi having made a snide remark about Kumiko when they were in their third year of junior high school. He was originally a horn player, but he gets to play the trombone after winning a game of rock-paper-scissors.
He notices minor internal conflicts within the concert band and notifies Kumiko, informing her a second year student had conflicts with a third year who hadn't practiced nor was adept at playing, the events of which that caused the number of second years to drop drastically.
In the park near her home, Shuuichi meets Kumiko, his childhood friend. After an awkward conversation between the two, Kumiko leaves, telling Shuuichi that she has decided to not join the school band.
Kumiko and Shuuichi have a good and friendly relationship. However, in junior high, he called her ugly and told her to never talk to him again. But that changed over the years as they can freely talk with each other about various topics, and they get along so well that they do not talk to each other using the polite form of speech, except for in public places. It is later revealed that Shuuichi has a crush on Kumiko, but she didn't notice it. Shuuichi and Kumiko become quite distant after some events, and have not had a meaningful conversation, except for the one before their competition performance, when Shuuichi kept telling Kumiko it was going to be alright after which they had a fist bump. However, they still see each other as musical peers, and have been using each other for inspiration to improve their playing.
Later in the light novels, Shuuichi tries to grow closer to Kumiko and nearly confesses to her the night before their final concert and he also gives Kumiko a hair decoration that’s shaped like the white flower Taki gave his wife before he proposed. Asuka mentions the hair decoration on Kumiko after her graduation ceremony and asks if it’s from her “boyfriend." Kumiko stumbles and eventually says yes which means that Kumiko also likes Shuuichi. In addition to this, she also confessed that she loves him, and they start going out later in the novel. In the anime, in season 2, Shuuichi's role is still a romantic interest, though he does not confess nor go out with Kumiko.
Canonically, Kumiko and Shuuichi are dating.
Hazuki had feelings for Shuuichi, but Shuuichi didn't realize it, so he only saw her as a friend, and they do have a good relationship. Later, at the Agata Festival, Hazuki confesses to Shuuchi but is rejected. He tells her that he already has someone else he likes. Hazuki realizes it's Kumiko, and says she will help Shuuichi be together with Kumiko instead. They become quite distant after this event, but he still considers Hazuki as a friend.
- Although he dislikes tomatoes, he is fine with ketchup.
- In terms of appearance, Shuuichi is very similar to Akihito Kanbara and Makoto Tachibana from the Kyoukai no Kanata and Free! series respectively, which are also animated by Kyoto Animation.
- Shuuichi initially played the horn during middle school but decided to take up the trombone when he started high school, saying that he always liked the jazz trombone.