The story takes place on Earth 33 years ago. The entire world has entered the all-mechanical age. At that time, the Earth had been completely polluted and became uninhabitable.
Five years ago, in 2042, in a certain city in a certain country that was completely isolated by steel and concrete (actually, I really want to write it as belonging to a certain country... But it will be harmonious = =), an unprecedented plague suddenly broke out, causing large areas of land to be polluted and abandoned. 3/4 Of the city's population was devastated and almost turned into a dead city. All the sick humans mutated and bitten the same kind.
Immediately afterwards, this terrible plague began to spread and eventually swept across the entire Eurasian continent. The desperate atmosphere of death floated in the sky across the entire continent...
Ps: The author has been reading a lot of Sword Art Online recently. I estimate that there will be some miscellaneous functions or systems similar to those in the game in the article. Just think of it as high-tech in the future world = =