In 2025, an RNA virus called "Bloodthorn" breaks out around the world, and infected people will mutate into extremely aggressive zombies within 72 hours. The virus is spread through blood and saliva, and initial symptoms include high fever, skin ulcers, and eventually organ failure. Three months before the end of the world, the global climate was abnormal, extreme weather occurred frequently, and collective deaths of animals occurred in many places. The scientific community attributed this to the "El Niño phenomenon", but in fact it was the incubation period of the virus.
