Two twins, divided by a fatal disease and a selective cure. Kasumi and her sister, Shizuku, contracted the Medusa virus, which gradually turns its victims to stone. While there is no cure, only Kasumi is chosen to enter a form of cryogenic stasis alongside 159 others until a remedy is discovered. At some point in an uncertain future, Kasumi awakens to find herself and the other suspended individuals in an unfamiliar world inhabited by violent monsters. Determined to uncover the mysteries of her current predicament and the fate of her twin sister, Kasumi fights to survive in a treacherous world.