Tsumugi Tōdō is the eldest of three sisters, with younger siblings Koyori and Kasane. She is a third-year student at Yamabiko South Academy, standing 1.65 meters tall with blonde hair reaching her hips and brown eyes; her figure features a notably large bust, often highlighted as the largest among female characters.

She works part-time as a waitress at the Yorozuyo Inn, a role she pursued out of aspiration rather than financial need, assisting guests and performing service tasks. This connection reflects her deep appreciation for Yamabiko's rural traditions and community life.

Her personality is marked by maturity, gentleness, and emotional stability. She frequently acts as a mediator within her social circle, offering advice and support, exhibiting a demeanor more mature than her peers, leading some to view her as a maternal or elder-sister figure. She demonstrates extensive knowledge of Yamabiko's local history, customs, and folklore, often sharing these stories. Her attachment to the town is profound, with no desire to relocate elsewhere.

Annually, she participates in the Futogoyama ceremony, underscoring her integration into the town's cultural practices. Her interactions are typically warm and nurturing, though she can display firmness when angered. Her initial encounter with Kazuma Hoshino occurs at the Yorozuyo Inn under awkward circumstances, which she handles with composure.

Within her family, she is depicted as responsible and caring, particularly towards her sisters. She remains largely indifferent to her reputation as an unintentional school idol, especially among male students. Her narrative role remains consistent as a stabilizing influence within the main cast, emphasizing her connection to Yamabiko's rural ethos and communal values.