When a deadly virus known as Medousa sweeps across the globe, turning people to stone with no chance of recovery, humanity finds itself on the verge of destruction. The only hope is the Venus Gate Corporation's shocking new plan: to put 160 people in cold sleep for up to one hundred years, or until a treatment is developed. Kasumi Ishiki is one of the fortunate to be selected, and though she fears being separated from her twin sister, Shizuku, the girls hope that they can be reunited in the future.

When Kasumi awakens, however, the world is not what she expected. The cold sleep facility is covered in thorns, and strange monsters start attacking them. Although most of those who have woken up die in the immediate confusion, Kasumi and a small group of survivors begin to investigate the maze-like facility and unravel the secrets of Medousa, as well as the true intentions of the Venus Gate Corporation.