Bantaro Sanbonmatsu is a student at Hontsuru Junior High and leads a gang including Kozaru, Ozaru, and later Shiro Ryujoji. He instantly develops romantic feelings for Jiyuu Nanohana upon meeting her, making frequent but unsuccessful confession attempts thwarted by bad luck. Undeterred, his persistent following of Jiyuu leads him and his gang to uncover her secret identity as the successor to Yagyu Jubei's legacy.

Driven by affection and loyalty, he resolves to support Jiyuu against her enemies, though his assistance often proves ineffective. This ineffectiveness is partly due to his lack of intelligence, a trait frequently noted by others despite his expected future role in taking over his family's traditional sake brewery.

His appearance features a distinctive element: the kanji characters on his shirt change dynamically to reflect his current emotional state, situational context, or conversation topic. Primarily serving as comic relief, his gang's antics contribute to the series' lighter moments. Across both seasons, his role remains consistent as Jiyuu's devoted but inept ally, embodying unwavering support despite personal limitations.