Eight hundred years ago, three thousand void gates opened in the skies all over the world, like three thousand differently colored eyes hanging in the sky, and countless monsters poured out from those eyes. There are giant species that can destroy cities and walls with one blow, are huge in size, and feed on human flesh; there are parasitic species that parasitize the human body, absorb human nutrients, and control humans to serve them; there are blood-sucking species that lurk in human cities, disguise themselves as humans, and feed on human blood... Overnight, humans became the lowest in the food chain.