Mizue Sakai is a minor character who appears in the Bakeneko arc, the third and final story of the anthology. She is the wife of Yoshiaki Sakai, the head of a samurai household that has fallen into financial ruin. Mizue is described as composed and domineering, with a commanding presence within the family. Her capricious desires and spending habits are indicated to have contributed significantly to the family's mounting debts, placing additional strain on an already declining house.

Mizue's role in the narrative is defined by her position as the mother of Mao, the first victim of the supernatural cat that haunts the Sakai estate. Mao's death serves as the inciting incident for the arc, drawing the Medicine Seller into the household to investigate the spirit. Mizue's grief and her reaction to the unfolding supernatural events drive much of the tension within the Sakai family. She is portrayed as a woman who is both protective of her remaining family and deeply entangled in the household's secrets and moral compromises.

Her key relationships are with her husband Yoshiaki, whose weak-willed leadership contrasts with her forceful nature, and with her daughter Mao, whose loss marks a turning point in the story. Mizue does not undergo substantial character development over the course of the arc; she remains a static figure representing the decay and guilt of the Sakai family. She possesses no notable supernatural abilities, and her significance lies in her role as a catalyst for the supernatural conflict and as a reflection of the family's moral decay.