Miki Saitō is Miyo Sasaki's biological mother and the former spouse of Youji Sasaki. She divorced Youji while Miyo was in elementary school, leading Miyo to believe her mother abandoned her. Miki resides relatively near Miyo and maintains occasional contact. Before the divorce, Miki was seen as a more nurturing parent, with Miyo notably cherishing her simmered taro dish. Following the separation and Miyo moving in with her father, Miki's demeanor shifted toward increased anger and frustration, though she retains underlying care for her daughter. Miki persistently expresses a desire to live with Miyo. Her insistence creates familial tension, particularly when she pressures Miyo to convince Youji to allow cohabitation. Miyo's rejection of this pressure triggers a pivotal argument, culminating in Miyo fleeing to a shrine bridge where she meets the Cat Mask Seller. After Miyo later vanishes following her transformation into a cat, Miki confronts Youji and his current wife, Kaoru Mizutani, at the Sasaki household. She accuses them of failing to understand Miyo's feelings and mishandling her upbringing. Kaoru challenges Miki's criticism by questioning whether Miki considered Miyo's feelings when she left the family. This accusation of hypocrisy provokes Miki to strike Kaoru. This altercation highlights Miki's unresolved guilt about her separation from Miyo and her complex maternal emotions. Her involvement centers on her strained relationship with Miyo and the consequences of her absence in Miyo's life. Her actions during Miyo's disappearance contribute to the story's themes of parental responsibility and reconciliation. Her name combines the characters for "beautiful" (美, mi) and "chronicle" (紀, ki), while her surname Saitō signifies "purification/religious purification" (斎, sai) and "wisteria" (藤, tō).