It is said that in Adventure City, a scholar named Sybel discovered the corpse of an ancient parasite near a mysterious altar deep within the forest ruins. From it, she extracted a rare substance known as the Abyss Virus. This virus not only accelerated the genetic evolution of living organisms but also possessed an incredibly strong vitality.

A wealthy and influential chairman named Carter, who was grief-stricken over the loss of his beloved daughter, invested heavily to establish Snow Mountain Biotech Corporation. He appointed Sybel as a senior executive and began researching the Abyss Virus in hopes of resurrecting his daughter.

Driven by desperation, Carter secretly initiated human experiments to speed up the process. However, during one of the trials, a catastrophic accident occurred, the virus leaked. Staff members and experimental subjects were infected one after another, and the outbreak quickly spread to the city. Soon, the entire world was plunged into chaos.

From that moment, the crisis erupted, and the human population dropped sharply.