800 years ago, 3000 dimensional gates opened across the entire world. In that moment, it was as if 3000 different colored eyes opened across the world as hordes of monsters swarmed out of these gates like tears.

Some could destroy city walls with one strike; They had bodies the size of a giant and fed on humans

Some latched onto humans, absorbing their bodies' nutrients and enslaving humans

Some infiltrated the humans' cities, disguising themselves as normal human beings while feeding upon human blood to sustain themselves.

In a night, the Human race fell to the bottom of the food chain.

The world had turned into a paradise for monsters…

From webnovel.com:

Lin Huang was a 15-year old boy from Earth, on a path to live his life in a world full of monsters. With his younger sister in his care, and given only 91 days to live, the odds were not in his favor at all… That is until, he killed a vicious vampire, purely by accident. With a twist in his tale, his life was changed completely. As he fought his way through this world with the help of his troops made of men and monsters, the boy sets his sights on a much larger ambition of becoming the greatest monster hunter in the world!