A college student named Rin moves into a new apartment in a gloomy, massive housing complex on the outskirts of town. She quickly realizes something is terribly wrong. Strange bugs roam the corridors, some floors appear completely neglected, and the cellars seem endless. Unable to terminate her lease, Rin begins investigating rumors of paranormal phenomena and strange deaths on her own. One night, she witnesses a giant insect emerging from a woman's arm. At a library, she learns these are called Ghost Bugs, life forms that have supposedly existed since ancient times. As she digs deeper, reports surface of a serial killer targeting young women, and Rin encounters rumors of mysterious red moths. Legend holds that seeing these moths foretells one's immediate death, and their appearance is linked to a massive chemical accident from forty years ago that left many dead.

The story then shifts to twenty-seven days earlier, following a high school girl named Tamahi. On her way home from school with classmates, she witnesses someone falling from the rooftop of a gigantic apartment building. The group rushes inside to find the victim, but there is no trace of anyone. As Tamahi wanders the building's labyrinthine corridors, she begins to feel watched and senses strange presences around her, eventually becoming lost in a distorted space-time continuum.

The apartment complex serves as the central setting, acting as a kind of portal to an nightmarish other world. The film weaves together Rin and Tamahi's investigations, exploring how their experiences connect to the Ghost Bugs, a series of deaths, and the building's dark secrets. The narrative unfolds as a surreal loop filled with disturbing creatures, body horror, and inexplicable twists, drawing comparisons to an infernal version of Alice in Wonderland.