The youkai sought to increase their personal power by turning themselves into cyborgs via a process that's been nicknamed "Frankensteining"¹, and they've each grown, one by one, as strong as any mortal human army. ¹The word the author uses is a pun on kikaika, or "mechanization," with the middle kai replaced with the one used in youkai. This is my best fit.

With the weak and fragile humans driven to the edges of the earth, the hierarchy of races on this planet has been completely reversed.

The youkai have dealt humanity a decisive blow, and there is no one who can challenge their dominion.

In this world, there is nowhere where "cannibalism is fine" is not the rule.