Sumida is a high school student with a short build and a fierce-looking face. He intentionally shaves off his eyebrows and often sports brightly dyed blonde hair. His family runs the "Sumida Tofu Shop," which he is expected to inherit after graduation, a responsibility stemming partly from his younger brother's plans to attend university. Working at the shop requires an early morning routine, and he is frequently seen wearing an apron. Academically, he struggles. Though reserved and quiet, Sumida demonstrates consistent care for his friends. He remains attentive to others even when distracted by interests like televised football. He forms deep emotional connections, evidenced by being moved to tears witnessing Yatora Yaguchi's dedication at the Geisai festival, and extends inclusivity, such as inviting Yotasuke Takahashi to explore the festival. His reserved nature coexists with impulsiveness, like his struggle with alcohol, leading to easy intoxication and vomiting. Sumida maintains a serious, long-term relationship with Megumi, who favors gyaru fashion. Their relationship is stable; she has met his parents, and they plan future marriage. He openly expresses physical affection, mentioning in class his habit of burying his face in her breasts. His enduring friendships include Koigakubo, a friend since elementary school; they joined the cooking club together in their sixth year. Artistically, Sumida participates in painting classes. While his process receives less focus than peers like Yatora, he relies on instinct and abstraction rather than technical overthinking. His art explores emotional vulnerability, expressing feelings hard for him to convey verbally. The resulting pieces resonate with viewers, providing him solace amid family obligations and socioeconomic background. His character subtly develops through interactions. Facing familial expectations to inherit the tofu business, he channels introspection and emotional expression into art, revealing growing self-awareness. Key moments, like his tearful response to Yatora's efforts, highlight increasing empathy and appreciation for others' passions, contrasting his otherwise skeptical view. He continues balancing his inherited future with personal relationships and creative pursuits.