Kozaru is a supporting character in Jubei-chan the Ninja Girl: Secret of the Lovely Eyepatch. He is a junior high school student in Hontsuru City and a member of the Ruffians, a small gang led by the brash and not especially bright Bantaro Sanbonmatsu. Along with his taller counterpart Oozaru, Kozaru forms a comic duo whose presence often lightens the tone of the story. His design carries monkey-like traits, with black hair and black eyes, and his short stature reinforces a playful, impish appearance.

Personality-wise, Kozaru is mischievous and given to silly behavior, yet he is noticeably more intelligent than his leader. Alongside Oozaru, he does not hesitate to criticize Bantaro’s impractical ideas or foolish actions, delivering blunt remarks with deadpan timing. Despite this sarcastic streak, he remains loyal and follows the gang’s schemes without serious protest, suggesting a motivation rooted in camaraderie and a taste for schoolyard mischief rather than any deeper personal goal.

Within the story, Kozaru serves primarily as comic relief. He and Oozaru appear whenever the Ruffians insert themselves into the main plot, usually in clumsy attempts to impress the protagonist Jiyuu Nanohana or to meddle in ongoing events. The pair is almost never seen apart, underscoring a tight bond that defines their shared identity as henchmen. Kozaru’s relationship with Bantaro is one of subordinate-by-circumstance, balanced by open mockery, while his partnership with Oozaru is one of seamless teamwork in both antics and commentary.

The character undergoes no significant development across the series, remaining a static fixture whose purpose is to provide humor and a recognizable gang dynamic. He possesses no special combat skills or supernatural abilities, operating simply as an ordinary student with a quick wit and a talent for pointed criticism. Kozaru reappears in the sequel series, Jubei-chan 2: The Counterattack of Siberia Yagyuu, continuing his role as a minor but consistently comedic presence.