Koharu Hidaka is introduced as a classmate of Haruo Yaguchi. Before her involvement with Haruo, Koharu was a quiet and studious student who knew little about entertainment beyond watching television dramas with her mother. Her life changed when she was drawn to Haruo’s carefree and passionate nature, which led her into the arcade scene. Initially learning video games as a way to connect with him, she soon developed a genuine and deep love for them. This passion transformed her personality, shaping her from a timid rule-follower into an assertive, independent, and highly determined young woman. She developed a stubborn streak and a playful, teasing dynamic with Haruo.

Her primary motivation throughout the series is her love for Haruo, which becomes deeply intertwined with her passion for gaming. She associates the joy of playing with the time she spends with him, leading to a fear that losing him would mean losing that happiness. This makes her a direct romantic rival to Akira Ono. The relationship between Koharu and Akira is complex; while they are competitors for Haruo’s affection, they share a mutual respect and a bond over their shared love of video games. Koharu is acutely aware of the deep connection Akira and Haruo share.

In Hi Score Girl II, Koharu is navigating her second year of high school. She has become a highly skilled gamer, recognized for her natural talent and adaptability. She excels at fighting games, mastering characters like Phobos from the Vampire series and Akuma from Street Fighter. Her skills develop to a competitive level that rivals Haruo’s. Her character arc in this season focuses on her emotional growth and her struggle to define her own identity apart from her feelings for Haruo. She must confront the reality of her unrequited affection and decide what she truly wants from life and from gaming. Her journey is defined by the tension between her kind-hearted nature and the fierce competitive spirit she discovered through arcade gaming.