Grandma Cat, also known as Neko Bāchan, is an exceptionally large and ancient catbus with a tail that functions as a propeller, enabling flight. Her immense scale resembles a cat-themed cruise liner, featuring multiple decks capable of transporting numerous totoro-like spirits. Each side of her structure displays thirty windows per row. She appears exclusively during a nighttime gathering of cat vehicles in a forest, where Mei approaches her with Totoro's assistance. When Mei asks if she is the Kittenbus's grandmother, the Kittenbus confirms with a meow. Mei introduces herself as the Kittenbus's friend and offers Grandma Cat a caramel candy. After a brief choking incident, Grandma Cat swallows the candy and exhibits contentment, leading to a mutual lick that establishes a bond between them.

As the oldest, largest, and matriarchal figure among catbuses, Grandma Cat embodies a gentle, grandmotherly presence despite initially intimidating Mei. Following the interaction, she departs with her spirit passengers, leaving Totoro behind while Mei and the Kittenbus observe her exit.