Oosawa Sachie (
Sachie has shoulder-length dark hair and brown eyes. During her employment at a post office, she wore a uniform consisting of a white dress shirt, a black vest, and a gray tie. Five years after the attempted post office robbery, she wore light makeup, a beige coat over a light purple shirt, and a knee-length gray skirt.
One Saturday afternoon in late 2020, Sachie was working behind the counter when a man entered the building and brandished a pistol, ordering the staff to fill his bag with all the money they had. Shocked by the man shooting one of her colleagues for pressing the alarm button, she stood frozen with terror when the robber pointed his gun at her, unable to take action as Shino intervened and killed the man in self-defense during their struggle. When her husband received a transfer after Mizue was born, Sachie moved to Tokyo, desiring to forget about the post office incident.
On December 15, 2025, Sachie was contacted by Kirigaya Kazuto, Shinozaki Rika, and Yuuki Asuna. Learning of how Shino had suffered from the post office robbery, she agreed to accompany them with Mizue to the Dicey Cafe to help the girl. The next day, Sachie and Mizue waited in a private room at the back of cafe until Shino was informed of the situation, before entering the main room. After introducing herself and her daughter to the confused adolescent, Sachie tearfully apologized to her for not contacting and thanking the girl for her actions, explaining how Shino had saved more than one life that day, as Sachie had been pregnant with Mizue at the time.