Before meeting Haruo Yaguchi in middle school, Koharu Hidaka was considered a plain and studious girl who focused solely on academics. She had little knowledge of popular forms of entertainment and spent her leisure time watching television dramas with her mother.

After Haruo introduced her to video games, Koharu’s world began to change. Initially drawn to gaming as a way to grow closer to Haruo, she soon developed a genuine love for games, becoming deeply engrossed in their worlds. This newfound passion transformed her personality making her more assertive, independent, and at times stubborn, as noted by characters like Doi and Miyao. Her dedication to gaming became intertwined with her feelings for Haruo, as she associated the joy that games brought her with him. This led to a possessive streak, as she feared that losing Haruo would also mean losing the happiness she found through gaming. Despite knowing Haruo did not return her romantic feelings, Koharu remained devoted to him. She also revealed a playful, teasing side, often taunting or lightly bullying Haruo in a way that reflected affection rather than malice.

By the events of Hi Score Girl Dash, Koharu has matured into a more reserved and seemingly emotionless individual. Although she has moved on from her feelings for Haruo, she carries the emotional scar of rejection. This loss of purpose led her to abandon gaming for a time. Nevertheless, she shows genuine care and dedication toward her work as a teacher and toward her students.

Koharu Hidaka is portrayed as an attractive young girl, often receiving attention and confessions from boys throughout the series. In her middle school years, she has short blonde hair adorned with a distinctive green hairband on the right side. Her features include long eyelashes and a notably developed figure for her age.

As she enters high school, Koharu initially grows her hair longer but later reverts to a shorter haircut. By the events of Hi Score Girl Dash set in 2007, Koharu’s appearance reflects her maturity, yet she continues to be regarded as highly attractive. She regains her longer hairstyle while retaining her signature green hairband from middle school. Her long eyelashes remain a defining feature, and she frequently wears a necklace with a red gemstone, which complements her various outfits.

Haruo Yaguchi
Although Koharu and Haruo grew up in the same town of Mizonokuchi, she first took notice of him during their second year of middle school when she saw him and some classmates leaving an arcade. Even before they became friends, Koharu was intrigued by Haruo’s simple-minded, carefree attitude and how much fun he always seemed to be having. As she began spending more time around him, her interest gradually deepened. Koharu realized she had fallen in love with Haruo during a Christmas party outside her family’s shop, after they exchanged gifts.

Akira Ōno
Koharu’s relationship with Akira is complex, largely shaped by their mutual connection to Haruo. Koharu views Akira as a romantic rival and believes that winning Haruo’s heart means surpassing Akira. Despite this tension, the two have no personal animosity and can be considered acquaintances. They officially meet in Round 11, although Koharu had seen Akira at the arcade before. Upon seeing Akira’s gaming skill firsthand, Koharu quickly recognizes that she would be outmatched in a direct competition.

Koharu invites Akira to play Virtua Cop, during which she tries to engage Akira in conversation about Haruo pushing boundaries by bringing up Haruo’s inferiority complex toward Akira. This visibly unsettles Akira, as reflected in her slipping gameplay when she accidentally shoots civilians in the game. Koharu further asserts herself by implying she will make a move on Haruo if Akira does not.

Their rivalry continues as both girls vie for Haruo’s affection, but outside of romantic competition, they share a mutual respect and bond over their shared love of video games.

Koharu Hidaka demonstrates a natural talent for video games, something even Haruo Yaguchi acknowledges, praising her adaptability and quick learning ability. While she initially limited her growth by practicing alone and letting her compassion influence her gameplay, Koharu’s skills significantly improved thanks to the guidance and support of Nikotama and the Mizonokuchi Force. With their help, she overcame these limitations and eventually reached a level comparable to Haruo’s.

Koharu plays a wide variety of games, but she is particularly known for using Phobos in the Vampire series and Akuma in Street Fighter, both characters reflecting her competitive spirit.

Her gaming setup includes: