Koharu Fujishiro is a young Japanese woman with orange hair styled in a ponytail and brown eyes. As the sole daughter of a samurai, her family background deeply influences her motivations. Her father's intense fixation drives her pursuit of independence, leading her to move into a dojo. This relocation serves dual goals: distancing herself from her father's control and positioning herself near her childhood friend, Shinjuro Tateoka, for whom she holds secret romantic feelings. Koharu justifies her temporary residence by paying rent, alleviating the dojo's financial strain while exploiting the absence of its master, Tesshusai Tateoka.

Her personality manifests as complicated and volatile. She exhibits a quick temper, frequently directing outbursts at Shinjuro and accusing him of perverse conduct. These confrontations often escalate to physical violence, channeling her frustrations. Underlying this behavior is a profound fear of losing Shinjuro's attention to other women, particularly Miren Hanafusa. Miren deliberately provokes Koharu by flaunting her femininity, intensifying Koharu's jealousy and existing insecurities about her physical appearance—including anxieties over her breast size and Shinjuro's preferences. Miren strategically exploits these vulnerabilities.

Koharu's actions and emotional reactions consistently reflect her deep investment in her bond with Shinjuro, alongside her struggle to assert autonomy while navigating romantic rivalry and personal doubts within the dojo environment.