Sadako Maki, Sho's elderly great-aunt, owns a house in Koganei, western Tokyo, where Sho stays temporarily before his heart surgery. Aware of family stories passed down through generations, she knows the house carries a history of Borrower sightings.

Acting as Sho's primary caregiver, she provides a quiet environment for his rest and expresses concern over his parents' absence due to work commitments, believing their presence would help him. Her demeanor is gentle and observant, though she remains unaware of the immediate activities of the Borrowers living beneath her floorboards.

Her ancestors constructed a detailed dollhouse specifically for the Borrowers, featuring functional elements like electric lights and ovens. This dollhouse later facilitates a connection between Sho and the Borrowers. After the Borrowers depart, Sadako discovers subtle traces of their existence, such as herbs left in a teapot, confirming their presence despite the absence of physical proof.

Her role is primarily supportive, offering stability for Sho during this critical time. She intervenes pragmatically to dismiss pest control personnel called by her housemaid, Haru, who becomes obsessed with capturing the Borrowers. Sadako's actions reflect her kind nature, focused on Sho's well-being while indirectly safeguarding the Borrowers' secret.