On one side, we have a guy living a boring and meaningless life meets Touko, a pretty girl, and it turns his life around. They get married, but three months later she tells him she is an alien from a far away planet, and that she must return to her home planet in a few days. Is she making excuses? Is she really an alien? Will he let their marriage end so easily?
On the other side we have Honda Haruno, a girl which has absolutely no other recollection other than being "sent" by her superiors to gather information about humanity; as a secret agent she needs to do her best as to learn as much as she can about society without giving away her true nature.... However on her first day of school she meets this boy "Isuzu", who has extensive information about UFOs, invaders from other space & related topics... Haruna not only is surprised to see that her cover has been blown out right from the start, but also she must know how this Isuzu fellow knew about her. Even though they don't realize it; Haruna and Touko are actually neighbors in the Akatoki Hoshi Residence... but, Is this all?