As a child, Natsuki doesn't fit into her family. Her parents favor her sister, and her best friend is a plush toy hedgehog named Piyyut who has explained to her that he has come from the planet Popinpobopia on a special quest to help her save the Earth. Each summer, Natsuki counts down the days until her family drives into the mountains of Nagano to visit her grandparents in their wooden house in the forest, a place that couldn't be more different from her grey commuter town. One summer, her cousin Yuu confides to Natsuki that he is an extraterrestrial and that every night he searches the sky for the spaceship that might take him back to his home planet. Natsuki wonders if she might be an alien too.

Back in her city home, Natsuki is scolded or ignored and even preyed upon by a young teacher at her cram school. As she grows up in a hostile, violent world, she consoles herself with memories of her time with Yuu and discovers a surprisingly potent inner power. Natsuki seems forced to fit into a society she deems a "baby factory," but even as a married woman she wonders if there is more to this world than the mundane reality everyone else seems to accept. The answers are out there, and Natsuki has the power to find them.

Dreamlike, sometimes shocking, and always strange and wonderful, Earthlings asks what it means to be happy in a stifling world and cements Sayaka Murata's status as a master chronicler of the outsider experience and our own uncanny universe.