Kio Kakazu, a clueless high-schooler living in Okinawa, meets a cat-eared girl named Eris at his grandfather's funeral, where she tells him her ship crashed nearby. Eris turns out to be a Catian, a feline alien sent to make first contact with Earth, and she promptly moves into Kio's home. As more Catians set up base around him, Kio is caught between his childhood friend Manami, the quiet Aoi, and rival agencies and dog-alien factions all circling Eris and her mission.