Haruka Mizuno is a third-year student at Hakodate Koyo High School and a member of the women's tennis club. Her physical attractiveness, academic capability, and polite, considerate personality draw the attention of admirers at school. Her relationship with Naoki Murakami begins when he witnesses her play tennis, instantly developing strong feelings, and she simply replies "yes" to his direct confession and request to date.

Following this, they mutually commit to gaining admission to the University of Tokyo (Todai) to stay together for university. Academically not a top student, concerns arise that she might jeopardize their shared goal. She devotes significant effort to her studies, working late into the night to improve her performance and exam readiness. Haruka approaches difficult situations with calmness and resilience, maintaining optimism and enthusiasm for the future despite setbacks.

The central tension revolves around the university entrance exams and the looming possibility of separation if one fails to enter Todai. Their relationship faces challenges, including Murakami's infidelity, which Haruka becomes aware of. Despite this, she demonstrates unwavering devotion to him and their commitment. Her emotional resilience allows her to navigate these personal difficulties while staying focused on their academic aspirations. The outcome of the entrance exams critically shapes her narrative journey and the future of their relationship.