Yuto Kawasagi works at a bookstore. She also lives as Hideko Katsuki, newly wed to renowned author Dai Katsuki. She is also Charon, a high-class prostitute working for her lover, gangster Michio Jigen. When Dai discovers her secret life, she disappears, and both Michio and Dai set out to find her.

Gabai Granny is based on the bestseller Saga No Gabai Baachan (Gabai Granny from Saga), which is penned by comedian Shimada Yoshichi as he recounts his childhood memories of growing up under the care of his grandmother.