Shinji Sakurai is a male student in Year 1, Class B at Namiuchigiwa High School, having previously attended Kondo Junior High. He possesses black hair, occasionally depicted as blond, and wears glasses. Sakurai rides with the Shōnan Bakusōzoku biker gang, participating alongside protagonist Yousuke Eguchi and core members Akira Ishikawa, Kakuji Marukawa, Yoshimi Harasawa, and Yoshiko Tsuyama.

Within the gang, he carries the designation "the narrowest man," suggesting a reserved nature. His story includes a romantic subplot explored in the narratives "Asagao no Kimi" and its sequels ("Asagao no Kimi 2" and "Asagao no Kimi 3"). These stories depict his "faint love," contributing to his character development and revealing a more vulnerable or introspective side alongside his gang activities.