Kio Kakazu finds a cat-like alien sitting at the buffet table. The alien introduces herself as Eris, and the two have a short conversation before Kio accidentally drinks beer and passes out. The next morning, Kio wakes up with a hangover and finds Eris sleeping half-naked next to him in bed. Kio's startled cry wakes her up, and she heals his hangover with a handheld device. Manami Kinjō and Maki Itokazu then visit Kio. After discovering that Eris is an alien, they both abruptly leave without saying why. It is later revealed that Manami is being recruited to become part of the CIA, Aoi is a Momiji for the Immigration Bureau of Japan, and Itokazu is the leader of an organization of SF fans called "Beautiful Contact", and they are all given orders to eliminate Eris.

Manami and Aoi watch Kio and Eris, both waiting for a good time to make their move. As they are waiting, however, Itokazu and "Beautiful Contact" attack Kio and Eris, and are about to kill both of them when Aoi disobeys orders to wait and saves Kio. She then moves to kill Eris, but Kio begs the Momiji (not knowing it is Aoi) to spare her. She obliges, but as soon as she leaves, Manami appears with CIA back-up, knocks Kio out, and captures Eris. Kio confronts Manami and begs her to help him find Eris. Manami contacts Aoi for extra help, and, receiving help from his uncle, Kio blackmails Itokazu and Beautiful Contact into helping as well. Together, they succeed in breaking into the military compound where Eris has been given to the DIA, only to find that she has already broken herself out.

Eris, along with other ranking officers, negotiate with the Japanese government. Upon returning to Kio's house, Manami and Aoi visi. They state their intention to leave, since the events of the previous episode marked them as traitors to their respective factions. Eris tells them that since Kio's house is now a Catian embassy, everyone inside is protected by Catian laws, and the two girls are invited to live there as well. Later, while the robotic servants are on guard duty and Manami and Aoi are bathing together, one of the robots is abducted by members of a yet unknown faction. Manami and Aoi spring into action, rescuing the robot. The next morning, Manami, Aoi, and Kio are hired by Eris as official embassy employees. Manami discovers Aoi's feelings for Kio, and offers to help her out, though Manami's reactions throughout the episode lead Aoi to suspect that she may have feelings for him as well.

When Kio wakes up, he walks in on Eris dancing and being abnormally energetic due to having smelled silver vine spirits, an Asian plant reported to be stronger than catnip. Dr. Dyureru appears and explains that Eris will soon be going into heat, causing her to have heightened senses, and congratulates Eris on having a mating partner on her first heat, much to Manami's outrage and Kio's embarrassment. She also assigns Eris a mission to go into Tokyo and "observe the human economy, technology, and culture", which, according to Eris, means to bring back a bunch of toys and games as souvenirs. On the train back, members of Underside of Kitten Paw separate Eris and Kio from Manami and Aoi, putting them to sleep and showing the sleeping Eris live to the screaming fans of Underside of Kitten Paw.

Kio takes Eris to a film shoot directed by one of his classmates, who is trying to film a sci-fi movie and would like Eris's help in getting footage of aliens without special effects. They decide that Eris looks too human, and instead ask her if they could use her ship or her robots. Meanwhile, Aoi wants to practice cooking to impress Kio, but due to her frequent failures she wastes a lot of food. At the same time, Manami wants to practice shooting, but she can't do it in Kio's backyard. Aoi asks for a Kio to be her taste-tester. Manami asks for a shooting gallery with a wide assortment of weaponry, and for an M134 Minigun in particular, which turns out to be too heavy for her to lift. She asks for a Kio to help her lift it, who tells her in a very Kio-like manner that he can't lift it.

The summer is over, and Kio, Manami, and Aoi all return to school. To their surprise, they find that Eris and Antonia have enrolled in the same class as them, as well as Antonia's maids. After school, Eris and Antonia garner excessive amounts of attention to the point that Antonia's maids scare off other students with uzis. Kio's club-mates ask him if he is going to the film camp, and asks Eris if she would like to go on the trip as well. As a result, Eris, Antonia, Aoi, Manami, and Antonia's maids all become members of the film club with the intention of going to the camp. Meanwhile, a group of Dogsian Assist-a-roids are robbing surrounding areas of electronic equipment, due to their inability to self-repair. The Dogsian ambassadors reveal a specially made Assist-a-roid that closely resembles a Catian Assist-a-roid.