Mimi is Asuna Watase's pet cat, sporting distinctive red markings on her fur. Asuna received Mimi as a memento from her late father. The cat frequently accompanies Asuna during solitary moments, including visits to a secret clubhouse where Asuna listens to mysterious radio transmissions. Mimi secretly follows Asuna into the underground realm of Agartha by hiding in her backpack, proving her loyalty. During their journey, Mimi assists in locating Shin after he is injured escaping the Izoku creatures. Upon reaching an Agarthan village, Mimi stays behind with the villagers when Asuna and Morisaki depart by boat. Mimi subsequently dies of natural causes. Following local customs, Shin, Manna, and the village elder offer Mimi's body to a Quetzalcoatl, one of Agartha's guardian entities. Later, near the Gate of Life and Death, Asuna briefly reunites with Mimi's spirit during a spiritual encounter. This happens alongside Asuna's vision of Shun, symbolizing closure for her past losses and reinforcing the film's theme of accepting mortality to move forward. Mimi's physical presence as a companion and her symbolic role in Asuna's emotional journey underscore themes of companionship and coping with grief. Her quiet presence and eventual passing serve as a narrative device reflecting the consequences of trespassing into the realm of the dead.