An "ash spore" disaster of unknown origin swept the world. These spores can corrode, transform and "activate" most plants in a very short time. Forests, grasslands, farmland and even urban green belts have become deadly "living jungles". Plants infested with spores can become extremely aggressive, secrete highly toxic gases or sap, and can even move and hunt for food. The surface is almost covered with activated plants, making it a dead zone. The surviving humans huddled in a few "underground cities" transformed from huge air raid shelters, abandoned military bases or underground facilities. The air requires multiple filtrations, food mainly relies on synthetic nutritional pastes and limited indoor cultivation, and resources are extremely scarce.
