Bantaro Sanbonmatsu attends Hontsuru Junior High as a member of the Unrefined Trio, a group that parodies delinquent stereotypes through exaggerated behavior. His most recognizable feature is an expressive shirt that dynamically displays kanji characters reflecting his immediate mood or thoughts—such as "idiot," "reckless," or "breasts"—providing a constant visual gag. He develops an unrequited romantic interest in protagonist Jiyu Nanohana soon after her arrival, leading him to attempt to deliver a love letter to her, though its outcome remains unknown. His comedic role peaks when he and his friends mistakenly attack Jiyu's father, Sai Nanohana, misinterpreting Jiyu's plea for him to "leave her alone" as a threat. In the second season, *Revenge of the Siberian Yagyu*, his narrative presence significantly decreases. Alongside the character Shiro, he becomes aware of this reduced role, explicitly acknowledging his status as a background figure. This self-awareness reinforces his function as meta-commentary within the story's dynamics.