Sohei Fujii transfers into Yuki's fourth-grade class and notices her unusual behavior and animal-like scent. His curiosity causes Yuki to avoid him, fearing he will uncover her secret. When he confronts her, she accidentally transforms into her wolf form and injures his ear. He protects her by claiming a wild wolf caused the injury, shielding Yuki from scrutiny.

Raised in a single-parent household, he feels displaced after his mother remarries and becomes pregnant. He confides in Yuki, believing his mother will no longer need him once the baby arrives. This sense of abandonment fuels his desire for independence, leading him to aspire to become a boxer or professional wrestler and live as a "lone wolf."

Two years later, during a severe storm that strands them at school, Yuki reveals her wolf form and confesses to attacking him. He calmly admits he knew her secret all along and reassures her, promising never to disclose it. This moment strengthens their bond, and Yuki affectionately calls him "Sou-chan."

He is characterized by his forgiving nature, loyalty, and perceptiveness. Despite Yuki's initial hostility and her secret, he remains steadfast. His observational skills allow him to notice subtle details like Yuki's scent or emotional distress. The film implies romantic feelings through his unwavering support and a parallel to Hana's initial encounter with the wolf man.

Physically, he has black hair and brown eyes. He typically wears casual clothing like striped shirts and shorts. His ear retains a scar from Yuki's attack, a permanent reminder of their shared secret.