Yukimi Yasuda appears as a secondary character in all official media adaptations: the manga, three television anime films, and the theatrical movie. A star athlete on the Seishū High School track club, she transferred at the start of the school year. Her athletic history precedes this move, alongside a longstanding crush on protagonist Katsuya Niimi dating back to their middle school years.

Confident, outspoken, and demanding, Yukimi stands as the direct opposite of the gentler, more reserved Yuri Nakao. Upon transferring to Seishū, she actively pursues Katsuya's affection, deliberately employing her female charms. This includes offering dates and promises of physical affection—such as kisses—as incentives for tasks, creating tension with Yuri.

Her primary narrative function centers on being Katsuya's romantic rival. Yukimi's persistent advances and rivalry with Yuri fuel the story's central love triangle. Despite her confidence and independence, every action reflects a singular goal: securing Katsuya's love to become his wife. She engages in supportive behaviors like cooking for him and cheerleading during his baseball activities to win his affection.

Beyond Katsuya, she interacts with Jirō Yamanaka, Kentarō Yamanaka's younger brother and a Seishū baseball team member. Jirō develops an unreciprocated crush on Yukimi, adding complexity to her relational dynamics.

Across all media, Yukimi remains driven solely by her romantic pursuit of Katsuya. She undergoes no significant development beyond this objective. The narrative consistently frames her actions and identity through romantic competition, contrasting her assertiveness with Yuri's passivity.