Earthlings recap

As a child, Natsuki survives family cruelty and sexual abuse by believing she is a magical alien, encouraged by her plush hedgehog Piyyut and her cousin Yuu, who also claims to come from another planet. Their intense childhood pact is forcibly broken. As an adult she enters a sexless marriage of convenience with Tomoya, who shares her refusal of the social system they call the Factory: the pressure to work, marry, have sex, and produce children. They return to her dead grandmother's mountain house and reunite with Yuu. Isolated there, the three try to abandon the rules and even the habits of ordinary human life. Their experiment descends into killing, cannibalism, and a shared conviction that they are transforming into aliens. The authorities eventually discover the devastated house and its survivors, while Natsuki interprets their altered state as preparation for departure to Popinpobopia.

Eleven-year-old Natsuki feels unwanted at home, where her mother favors her older sister Kise and treats Natsuki as a source of trouble. She finds safety in a private belief that her plush hedgehog Piyyut comes from the planet Popinpobopia and has made her a magical girl. At the family's summer gathering in the mountains, she reunites with her cousin Yuu. He says he too is an alien, and the two children form an intense pact based on their shared difference from the adults around them. Back at school, Mr. Igasaki exploits Natsuki's isolation and sexually abuses her. She tries to survive by treating him as an enemy outside the category of ordinary humans. Her family does not become a source of protection, strengthening her conviction that she must defend herself through the alien identity she shares with Yuu.

Years later, Natsuki has built an outwardly acceptable adult life without accepting its values. She and Tomoya marry as a mutual defense against relatives who demand conventional adulthood. They do not want sex or children, and privately describe society as a Factory that turns people into workers and reproductive bodies. Pressure intensifies when their families discover that the marriage is not functioning as expected. Natsuki's childhood history remains active beneath her controlled routine: she still possesses Piyyut, remembers Yuu, and associates her grandmother's house at Akishina with the only place where she once felt understood. The couple decide to leave the city and return to that mountain house, seeking space outside the demands they reject.

At Akishina, Natsuki and Tomoya reunite with Yuu. The childhood bond does not simply resume: adulthood, shame, and years of enforced normality have changed him. Even so, the three recognize a shared desperation to escape the Factory. They isolate themselves in the house and begin treating ordinary social rules as arbitrary controls rather than necessities. Their attempt to make a new life grows harsher as food, hygiene, sexuality, and personal boundaries lose their familiar meanings. What began as Natsuki's private childhood defense becomes a collective worldview. The trio increasingly speak and act as if rejecting human society also requires rejecting their own humanity.

The experiment at Akishina reaches a violent end. Natsuki, Tomoya, and Yuu remain united against relatives who come to recover them and restore the social order they have rejected. The confrontation produces deaths, and the isolated trio cross the final taboo by eating human flesh. Their living conditions and bodies deteriorate while their belief in alien transformation becomes more complete. When police and other outsiders finally enter the house, they encounter death, cannibalism, and survivors who no longer understand themselves as ordinary people. Natsuki perceives bodily changes in herself and her companions and interprets the approaching outside world through the promise of Popinpobopia. The novel closes within that perception: after enduring abuse and coercion, she believes they have escaped the Factory by becoming alien, though nothing outside their shared reality verifies that a spaceship has come.

At the Akishina house, Natsuki, Tomoya, and Yuu cut themselves off from the families and institutions they call the Factory. Their effort to discard ordinary rules becomes violent and physically destructive. When relatives come to force them back, the confrontation ends in deaths, and the trio consume human flesh as they pursue an increasingly literal idea of becoming nonhuman. By the time the authorities enter the house, they find a scene of death, filth, and cannibalism. Natsuki experiences the trio not as defeated social outcasts but as beings whose bodies and perceptions have changed, ready for a spaceship from Popinpobopia. The closing perspective does not confirm an extraterrestrial rescue; it leaves her alien identity as the reality through which she interprets the extremity of trauma, shared delusion, and resistance.