Five years ago, where all was normal day-to-day activities. The higher-class society filled with many rich people wanted to find a way to make themselves immortal to enjoy all their wealth. Not knowing if the serum would even work out, they used many of the lower class. Not much time passed, and an epidemic started coming through. The infected turned into monsters and almost wiped out all of humanity. Luckily, many survived but are still fighting with the monsters.