Haruka Mizuno is a central character in the anime Tokyo University Story, portrayed as a third-year student at Hakodate Koyo High School and a member of the school's women's tennis club. She is notable for her physical attractiveness, strong academic capability, and a polite, considerate personality, which together draw the attention of many admirers at her school. Her life takes a significant turn when she is first noticed by her classmate, Naoki Murakami, who sees her playing tennis and instantly develops strong feelings for her. When he directly confesses and asks to date her, Haruka gives a simple reply of "yes," agreeing to begin their relationship.

From the start of their romance, Haruka and Naoki share a powerful and defining motivation: they mutually commit to gaining admission to the prestigious University of Tokyo, often referred to as Todai, to ensure they can stay together for their university years. This shared goal becomes the central pillar of the story, and Haruka's role is largely defined by her determination to achieve it. Unlike Naoki, who is depicted as a naturally gifted "triple threat" of good looks, a sharp mind, and outstanding motor nerves, Haruka is not initially portrayed as a top-tier student. This academic disparity creates a core tension in the narrative, as concerns arise that her performance might jeopardize their shared dream.

Nevertheless, Haruka is defined by her resilience and dedication. Facing the possibility of separation if she fails the entrance exam, she devotes significant effort to her studies, often working late into the night to improve her performance and exam readiness. She approaches difficult situations with a notable calmness and maintains an optimistic and enthusiastic outlook for the future, even when faced with setbacks. Her emotional strength is further tested when she becomes aware of Naoki's infidelity. Despite this personal hardship, she demonstrates unwavering devotion to him and to the commitment they made to each other, choosing to navigate these difficulties while remaining focused on their academic aspirations.

Haruka's key relationships are primarily with Naoki Murakami, her boyfriend and the catalyst for her journey, but she also interacts with her wider social circle, including friends like Sano Hayato and Suzuki Eri, who are part of their high school environment. Her development throughout the story is intrinsically tied to the pressure of the university entrance exams and the emotional turmoil of her relationship. She grows from a admired but academically average student into a fiercely determined individual who learns to balance her personal feelings with her long-term goals. Her notable abilities are not supernatural or combat-oriented but rather lie in her interpersonal grace, her physical skill as a tennis player, and her cultivation of strong study habits. Ultimately, Haruka's emotional resilience and her capacity for hard work are her most defining strengths, shaping her character as she strives to secure a future with the person she loves. The outcome of the entrance exams critically shapes her narrative journey and the future of their relationship.