Midori is a high-school-aged lesbian who has just been rejected, driving away one of her few friends. In the world right now, there are creatures called "Extraneous" that appear out of nowhere, kill people, and disappear again. No one remembers when they started appearing, but the chance of being killed by one is about the same as the chance of dying in a car accident. Midori's mother was killed by one a year ago, and not only is her father rarely around, he's also deeply in debt. She gets attacked by an Extraneous on her way home, but is saved by a mysterious girl who claims that she's a god. Midori names her Hitsuji (sheep) because of her horns, and takes the girl in. They start a website, Hitsujiya, an Extraneous-fighting service provided by Hitsuji.