The story revolves around Kakazu Kio, an ordinary high school freshman living in Okinawa. A girl with cat ears appears before him during a memorial service for one of his family ancestors. The girl calls herself Eris and claims to be an alien. Before long, fanatical alien worshippers and a mysterious government agency are in hot pursuit of Eris, but Kio's childhood friend Manami — who wants to follow in her father's footsteps in the CIA — captures Eris. Kio finds himself having to protect Eris from everyone.