Tatsuko Gakumazawa is a classmate and friend of Illyasviel von Einzbern, alongside Suzuka Tsukimura, Nanaki Moriyama, Mimi Katsura, Miyu Edelfelt, and Chloe von Einzbern. Her family runs a martial arts dojo, and she works part-time jobs at a beach and during festivals. Standing at the stature of a second-grade elementary student, Tatsuko ranks as the least athletic among her peers. Despite her family's martial arts background, she displays striking physical ineptitude, often triggering accidental mishaps like injuries during dodgeball games. This clumsiness contrasts with her absurdly high resilience, allowing her to walk away from severe impacts with only superficial scrapes.

Her personality radiates childish immaturity, routinely sparking comedic chaos. She idolizes her father and brothers for their physical strength, a reverence rooted in her dojo upbringing. Across all franchise media—including manga seasons, anime adaptations like *Undoukai de Dance!*, *2wei!*, *2wei Herz!*, *3rei!!*, and *Prisma☆Phantasm*, plus specials—she remains a consistent comedic supporting figure. Informally dubbed Fuyutsuki City's "Village Idiot," she embodies lighthearted comic relief without undergoing significant development or backstory expansion.