The story follows Kakazu Kio, a typical high‑school freshman living in Okinawa. During a memorial service for one of his ancestors, a girl with cat ears appears before him and introduces herself as Eris, claiming to be an alien. Before long, zealot alien worshipers and a mysterious government agency pursue Eris. Kio’s childhood friend Manami, who hopes to follow in her father’s CIA footsteps, captures Eris. Faced with relentless pursuit, Kio must protect Eris from everyone.