Hidaka Koharu begins as a studious middle schooler dedicated to academics, her sole hobby watching television dramas with her mother. Her life shifts dramatically upon meeting classmate Haruo Yaguchi in their second year. Initially exploring video games to bond with him, she develops an authentic passion for gaming, transforming her reserved nature into a fiercely stubborn and competitive spirit. This emerges in her pursuit of Haruo’s affection and her mastery of fighting games like *Street Fighter II*, where she displays natural talent with characters such as Zangief and Phobos. Her romantic feelings for Haruo create tension within a trio involving Akira Ono, fueling the series’ core emotional conflict.

Koharu possesses conventional attractiveness, featuring blonde hair secured by a green band and distinctive eyelashes. Her style evolves in high school, including longer hair. Her personality blends politeness and rule-following with intense competitiveness in gaming and romance. She exhibits subtle sadistic tendencies, teasing Haruo without malice. Her self-worth becomes entwined with gaming; losing Haruo threatens to strip gaming of its joy.

As a 28-year-old in *Hi Score Girl Dash*, Koharu teaches at her former high school, now co-ed. Emotionally guarded after Haruo’s rejection, she initially avoids gaming. Her intrinsic connection resurfaces through mentoring troubled students—Miwa Katagiri, Shinji Yamai, and Mirai Hoshina—using fighting games like *Vampire Savior* to build their confidence and resolve struggles. She extends this approach to reconcile the school principal with her estranged son. Professionally protective, she adopts a stern demeanor defending students but declines romantic pursuits, rejecting matchmaking. Briefly rekindled feelings for Haruo channel into supporting his academics and aiding Akira Ono’s family reconciliation.

Koharu’s gaming skills remain formidable in adulthood, defined by an uncompromising playstyle after switching to Bishamon in *Vampire Savior*—a symbolic choice reflecting past heartbreak. Only colleague Doi Genta initially knows her gaming history, yet her expertise proves vital in mentorship. She ultimately embraces a teaching philosophy harnessing video games for personal growth and connection, mirroring her own transformative journey.