Grand-mère is a significant supporting character introduced in the latter part of the anime series. Her most prominent and defining action occurs during a critical moment when her group of survivors faces complete annihilation. As the leader of a settlement named Wendelstein, she provides refuge for several main characters, including Kunagi and Kaoru, in a world overrun by a virus that transforms humans into cats.

In terms of personality, Grand-mère is defined by her profound selflessness and protective instincts. When the settlement comes under a massive attack by a horde of cats controlling larger animals, with all hope seemingly lost, she makes a monumental decision. To save her group, she chooses to sacrifice her own humanity by willingly allowing herself to be transformed into a cat. Her motivation is clear and resolute: the survival of the people under her care is paramount, even at the cost of her own human identity.

This sacrifice is not just a physical transformation but a strategic gamble. After becoming a cat, Grand-mère retains enough of her consciousness or gains a unique ability to verbally communicate with the other cats. She uses this opportunity to reason with them and convince the pack to leave the survivors alone. This action reveals that the feline threat, while devastating, is not driven by malice. The cats are portrayed as seeking play and companionship, largely unaware of the chaos and destruction they cause, a fact that Grand-mère is able to confirm through her direct communication with them.

Within the story's narrative, Grand-mère serves as a mentor and caretaker figure. Her role is to provide a safe haven for the protagonists, representing one of the last organized bastions of humanity fighting to maintain order. Her key relationships are with the main characters she shelters, as well as the other members of the Wendelstein settlement, whom she is determined to protect. Her development arc is brief but powerful, culminating in her ultimate act of heroism. She transitions from a background leader to a central figure whose sacrifice directly resolves a major threat to the group, showcasing that even in a world of absurd horror-comedy, genuine acts of bravery have real and lasting consequences. Her notable ability, gained through her sacrifice, is the power to communicate with cats in their transformed state, a unique trait that allows her to broker peace where human weapons and defenses had failed.