The story takes place in a modern city. In seven days, a global disaster known as the Red Fog will break out. As the Red Fog blankets the land, living things will mutate into savage "variants." The order of human civilization will collapse, and the world will enter an apocalypse where the strong prey on the weak. Later, it is revealed that the Red Fog is not a natural phenomenon, but a virus released by an advanced civilization as a form of "ecological modification," designed to select and drive evolution.
