Mouse appears exclusively in the 1979 animated short film *Unico: Black Cloud and White Feather*. He is a resident of a city heavily polluted by emissions from a nearby factory. Mouse interacts directly with Unico and a young girl named Chiko, who suffers from an illness caused by the pollution. He demonstrates concern for Chiko's deteriorating health and acts as an intermediary between her, Unico, and the wider community suffering from the factory's pollution. His presence highlights the environmental devastation caused by industrial neglect.