Tatsuko Gakumazawa is a classmate and friend of Illyasviel von Einzbern, Miyu Edelfelt, Suzuka Tsukimura, Nanaki Moriyama, and Mimi Katsura. Her family runs a martial arts dojo, and she takes part-time jobs at beaches and festivals. Despite this martial arts heritage, Tatsuko lacks physical talent or athletic ability, consistently standing as the weakest among her peers with notable struggles in activities like dodgeball. She functions as comic relief through childish, immature behavior that unintentionally creates trouble for others, earning her the unofficial label of Fuyutsuki City's "Village Idiot". Paradoxically, Tatsuko exhibits extreme resilience, often escaping serious harm from incidents that would typically cause significant injury, a recurring trait in her appearances. Her energetic yet unfocused nature is captured by the observation that she possesses "many talents, all of which are useless". In the OVA *Prisma Phantasm*, she features alongside the main cast in surreal comedic segments, reinforcing her established group role. Across the series, films, and spin-offs, her character shows no significant development or expanded backstory beyond these traits.