While the spaceship Frontier attempts to return to Earth, it intercepts a mysterious signal from an unknown intelligent lifeform. First Officer Haruna Tanaka descends to planet Parnas with her crewmates to investigate, but they are captured by aliens. Haruna is examined, violated, and assaulted. Later, her memories are erased and she safely returns to Earth. From that day on, she suffers from nightmares and strange physical changes. One day, a fellow crew member, Yokota, regains his memories and reveals a horrifying truth: the aliens they encountered are terrifying parasitic organisms that reproduce by invading human bodies—and they already have alien lifeforms growing inside them. The parasite inside Haruna gradually consumes her body, growing steadily until it prepares to burst forth as a monstrous creature. To stop the alien's spread, Haruna faces an ultimate decision—sacrificing her own life as the host. She now stands before this agonizing choice.