Mizue has brown eyes and dark hair tied in two braided pigtails. She wears a kindergarten uniform consisting of a white blouse, a dark blue skirt, and a red bow pinned at the collar. She also carries a yellow pochette slung over her shoulder.
On December 16, 2025, Mizue accompanied her mother to the Dicey Cafe after Sachie was contacted by Kirigaya Kazuto, Shinozaki Rika, and Yuuki Asuna the previous day. Having waited for the right moment in a private room at the back of the cafe, Mizue and Sachie entered the main room once Asada Shino was informed of the situation. As Sachie explained to the confused adolescent how she had been pregnant with Mizue the day a man attempted to rob the post office where she used to work five years prior, the little girl followed her mother in repeatedly bowing to Shino. After Kazuto declared to Shino that she had the right to consider the lives of those she saved, Mizue withdrew from her bag a handmade crayon drawing of herself with her parents, addressed to Shino. After giving the drawing to Shino, the child carefully recited her words of gratitude to the older girl for saving her and her mother. Mizue then gently reached for and held Shino's hands when the girl began crying.