"Medusa" has erupted into a worldwide plague. To shield a handful of people from the lethal pathogen, authorities decide to place them in cryogenic stasis, hoping that a cure will be found while they lie dormant. Kasumi, a sixteen‑year‑old girl, is among the 160 selected and escorted to the Cold Sleep Capsule Center (CSCC) hidden inside an ancient citadel. Though she knows survival is uncertain, Kasumi accepts the procedure and falls asleep, clutching hope of reuniting with her twin sister Shizuku, who is also infected. When the sleepers finally awaken, they discover that the CSCC has transformed: a once‑majestic fortress now lies overgrown with thorny vines, and the revived are immediately attacked by mysterious beasts. How many years have passed? Where did these monsters come from? What fate has befallen the world?
Left in a labyrinth of unanswered questions, the saga of seven survivors begins. The survivors must navigate the ruins, uncovering clues to the origin of the plague and the monsters that stalk them.