As a child, Natsuki doesn’t fit in with her family. Her parents favor her sister, and her best friend is a plush toy hedgehog named Piyyut, who talks to her. He tells her that he has come from the planet Popinpobopia on a special quest to help her save the Earth.

One summer, on vacation with her family and her cousin Yuu in her grandparents’ ramshackle wooden house in the mountains of Nagano, Natsuki decides that she must be an alien, which would explain why she can’t seem to fit in like everyone else.

Later, as a grown woman, living a quiet life with her asexual husband, Natsuki is still pursued by dark shadows from her childhood, and decides to flee the “baby factory” of society for good, searching for answers about the vast and frightening mysteries of the universe—answers only Natsuki has the power to uncover.