College student Aki is startled when a teenage girl abruptly enters his Tokyo apartment, behaving as though he ought to recognize her. Once the reality emerges, the scenario proves even more bizarre. The "teenage girl" is actually Mill, his cherished pet cat from his home in Kyushu, who is apparently an 86-year-old "monster cat" capable of shifting between feline and human forms. Will Aki manage to integrate his supernatural pet cat into his mundane college life?