Yuusuke Azumi, a teenage student and friend of Norimichi Shimada, competes against him in a swimming race for a date with Nazuna Oikawa. Winning the race earns him Nazuna's invitation to the summer festival. Though he agrees to meet her, he later avoids the date. He sends Norimichi to his family's hospital, where they live, using Norimichi's minor injury as an excuse for Norimichi to cancel on his behalf, driven by internal conflict over his feelings and social pressures.

When altered timelines shift the race's outcome, Yusuke discovers Norimichi and Nazuna together. He lashes out in hostility, perceiving betrayal, and initiates physical confrontations with Norimichi. During one encounter at a lighthouse, his aggression accidentally sends both Norimichi and Nazuna tumbling from the structure. His anger persists across timelines, especially upon witnessing Norimichi and Nazuna trying to evade her family.

Physically, Yusuke is a male teenager with black hair cut to ear length and black or grey eyes. Following Norimichi and Nazuna's disappearance at the film's conclusion, Yusuke's fate remains untold.