Kenji Yanagimoto is a male student at Ousai Private Academy, progressing from first-year to second-year status during the series timeline, aged 15-16. He has short grey-black spiky hair and consistently wears half-rimmed glasses that obscure his eye color. His height approximates Takatoshi Tsuda's, and he is typically seen in the standard school uniform with a tie.

Unlike Takatoshi, who chose Ousai for its proximity, Kenji deliberately enrolled after the academy transitioned to co-education, motivated by its heavily skewed female-to-male ratio. Aria Shichijō classifies him among the "harem-seekers," as Kenji confidently expected romantic attention—specifically Valentine's chocolates—due to the gender imbalance. Takatoshi directly challenged this assumption, arguing minority status alone wouldn’t guarantee female interest.

Kenji expressed overt jealousy over Takatoshi’s vice presidency of the female-dominated Student Council and openly wished to assume the position. However, when Takatoshi seriously offered to relinquish the role, Kenji immediately retracted his desire, acknowledging the workload and difficulties involved. His refusal notably irritated Takatoshi.

Despite initial harem-seeking motivations, Kenji evolved into a comparatively grounded teenager relative to the series' more eccentric personalities. As one of the few recurring male students with consistent dialogue, he demonstrates perceptiveness about social dynamics—such as identifying Takatoshi’s unjustified self-deprecation during a class tennis activity and calling out his flawed reasoning.

Kenji maintains a friendship with Takatoshi as a male classmate. Narrative elements occasionally pair him with Chiri Nakazato, a tomboyish judo club member, implying an association between them.