College student Aki is shocked when a teenage girl suddenly barges into his Tokyo apartment, acting as if he should know her. When the truth becomes clear, the situation is even stranger. The "teenage girl" is actually his precious pet cat Mill from his home in Kyuushuu, who is apparently an 86-year-old "monster cat" who can change between cat and human forms. Will Aki be able to fit his supernatural pet cat into his ordinary college life?