Are you confident that your home is secure when you are away? Have you noticed subtle changes upon your return, such as a cushion out of place or a juice bottle partially empty? You might dismiss these as tricks of the mind, but for Youko, they are a chilling reality. She is no ordinary young woman, having fled her previous life to live underground, infiltrating homes during the owners' absence.
Initially, this lifestyle is exciting and free, but Youko soon discovers a subculture of "leeches," others who live like her. Violence permeates their existence, as they fight for control of homes, or "nests," engaging in brutal wars for territory, leading to bloody vendettas and devastating consequences.