The drifting classroom

Out of nowhere, a Japanese elementary school is transported out of the world they know, and into a nightmarish wasteland. Have they gone to another planet, or is this toxic world actually a vision of Earth's future? Soon, the students and teachers must struggle to survive in impossible conditions, besieged by terrifying creatures and beset by madness. Pursued by grotesque mutants, Sho and his friends flee back to the school, where more horrors await! Barricaded against the nightmares outside, the students must perform an emergency medical operation under the most primitive of conditions. As the survivors' resources dwindle, the countdown draws closer and closer to the end--