Sugimura is a junior high school student and childhood friend of Shizuku Tsukishima, friends since their early years. He attends the same school as Shizuku and Yuko Harada, sharing a close friendship with Yuko. He has brown hair and black eyes and is typically seen in a standard school uniform.

Friendly and helpful, Sugimura exhibits significant obliviousness to romantic cues. This trait becomes central when he assists a baseball teammate in delivering a love letter to Yuko, unaware that Yuko harbors feelings for him. Yuko's subsequent emotional outburst and avoidance leave Sugimura confused, requiring Shizuku to explicitly explain that Yuko's distress stems from her romantic interest.

During this conversation, Sugimura reveals his own longstanding romantic feelings for Shizuku. Shizuku gently but firmly rejects him, emphasizing their platonic relationship and her loyalty to Yuko. Sugimura accepts this rejection with visible sadness, agreeing to maintain their friendship without further mention of his feelings.

Sugimura reconciles with Yuko afterward. He apologizes for his role in the misunderstanding and informs his teammate that Yuko is not interested. Yuko likewise apologizes for her earlier outburst, and Sugimura accepts her apology. Later, when Seiji Amasawa visits Shizuku at their school, Sugimura displays a subdued and somber reaction, keeping his emotions private.

Sugimura's involvement diminishes after these events. His final appearance occurs in the film's closing credits, implying a positive resolution to his relationship with Yuko and suggesting they may have formed a romantic connection.

Outside the central romantic subplot, Sugimura participates in his school's baseball team, primarily as a ball boy rather than a main player. His personality combines a desire to impress his female friends with a distinct shyness in expressing his own emotions. His surname combines "cedar" (杉) and "town/village" (村), reflecting common Japanese naming conventions.