Since losing her husband, single mother Kaori Hanazawa has been working as a building cleaner while raising her only daughter, Kiriko. Smoking is the only thing that comforts her in her unchanging daily life. However, at her workplace, the smoking room has been downsized due to the policy of the newly appointed vice president. The price of cigarettes has been raised, and an ordinance banning walking cigarettes has been introduced. Then, one day, their daily life suddenly changes. Unknown creatures fly out from numerous spheres sent from outer space and begin to parasitize and manipulate humans. The spheres fell on the roof of Kaori's workplace, and within a few hours most of the employees had become parasites. Trapped in the building, the colleagues discover that the space creatures are vulnerable to cigarette smoke. But this is only the beginning of the fight to the death.
