Koharu Hidaka begins as a reserved, academically driven middle school student with no hobbies until a pivotal encounter with Haruo Yaguchi, who frequents her family’s shop to play video games. His presence ignites her curiosity about gaming as a bridge to connect with him, leading her to discover an innate talent for titles like *Street Fighter II* and *Samurai Shodown*, where she often matches Haruo’s prowess.

Initially shy and rule-bound, she transforms into a fiercely competitive gamer, driven by a determination to preserve her bond with Haruo. This shift reveals a stubborn streak and a subtly sadistic side, expressed through playful teasing during matches. Beneath her growing confidence lies vulnerability, as she grapples with unrequited feelings and fears losing the person who brought joy into her life.

Years later, in *Hi Score Girl DASH*, Koharu returns to her alma mater—now co-ed—as a middle school teacher. At 28, she appears emotionally distant, having abandoned gaming after Haruo’s rejection. Yet mentoring students rekindles her passion, guiding her to employ gaming as a tool to help them navigate bullying and family strife. Her classroom blends disciplined authority with secret gaming sessions, reflecting her conviction that games foster resilience and growth.

Her family’s arcade-equipped shop laid the foundation for her gaming journey. Relationships with peers like Akira Ono, her romantic rival, and mentor Felicia Nikotama shape her path. Though she moves beyond her fixation on Haruo, faint echoes of her feelings linger, channeled into nurturing others—even aiding Akira’s mother in reconnecting with her daughter through shared gameplay.

Koharu’s appearance evolves from youthful short blonde hair with a green headband to a polished, approachable adult style with longer locks. Her journey from a lovestruck teenager to a compassionate educator mirrors themes of self-discovery, illustrating how past relationships quietly sculpt identity and purpose.