In 2016, a large-scale plague broke out around the world. A new type of deadly virus left scientists around the world at a loss. People did not know the source of the plague and its antibodies. This highly lethal virus swept every country on the earth, causing large-scale human deaths. What is even more terrifying is that the dead were automatically "resurrected" after 2 hours. This virus, called Satan, can control the brains of the dead, manipulate the behavior of corpses, and turn them into zombies that devour human flesh.
The number of zombies has increased exponentially, and only a few people have survived on the earth. As a result, human history has entered a new era - the first year of the apocalypse. In times of crisis, the provisional governments of various countries united and used remaining supplies to establish several "clean zones" isolated from the outside world on various continents in order to accommodate surviving personnel, build armed forces, and fight for human survival. These clean zones were called "fortresses."