Eiji Busujima, a reformed delinquent with sanpaku eyes and a naturally intimidating glare, battles constant misjudgment due to his threatening exterior. His blond hair, red hoodie peeking from a gakuran, and sturdy frame mask a gentle soul drawn to senryū poetry. This passion, sparked by middle-school encounters with Nanako Yukishiro at a senryū gathering, leads him to join the Literature Club, defying expectations tied to his "poison island" surname—a lingering echo of his rebellious past.

Once ostracized for his rough demeanor, Eiji slowly wins peers over through quiet kindness and relentless self-improvement. His bond with Nanako deepens from shared literary interest to mutual affection, though his initial obliviousness to her hints delays their heartfelt confession during a class trip. Family anchors him: he prioritizes his younger sister Hanabi’s happiness but hesitates to expose Nanako to his eccentric parents, Akira and Kazue, whose quirks contrast their son’s guarded sincerity.

Eiji’s evolution—shedding societal labels to embrace vulnerability—mirrors his clumsy yet earnest senryū attempts, symbolizing growth and connection. Honest and fiercely protective, his gullibility often lands him in comedic traps set by friends Amane Katagiri and Koto Ōtsuki. Academically, he ranks second in school not for grades but the stark contrast between his delinquent image and bookish club affiliation.

A lover of meat-heavy meals, Eiji’s tenderness extends to a pet rabbit featured in both manga and anime. Despite progress, remnants of his past surface in abrupt speech or impulsive acts, like smashing his phone in frustration. Koto’s teasing and Amane’s meddling in his romance underscore his integration into social circles, charting a journey from isolation to belonging, fueled by unwavering loyalty to those he holds dear.