The monsters have taken over earth! 115 years ago.
After multiple generations of war, subjugation and conquest, man- and monsterkind has learned to coexist together - somewhat. Make no mistake, the demons, feyfolk, angels and their like continue to run the world, but to build and maintain a stable empire, dogmatic tyranny gave way for pragmatic mutualism. After mankind had been completely overthrown within months, monsters turned their ire towards rivaling factions, making up the bulk of the conflicts that arose since the dawn of the apocalypse. And while the three remaining monster factions hold as much resentment for each other as they did at the beginning of the apocalypse, they all grew to temper their ideals and granted the humans they once enslaved more rights, moving the civilized parts of the world towards a society where the former apex species of earth can live relatively stable - though mostly oppressed - lives.
One of the main reason for monster-human collaboration is Orgone - a supernatural resource almost exclusively generated by greatly intelligent lifeforms (in other words, human). As the only form of nourishment for monsters in this plane, it was once harvested from the brains of their victims, but after accepting the unsustainability of their ways and the strain on their resources threatening their position in the power struggle, the role of humans changed from pure cattle to servant to even equal, depending on where you live. After all, why engorge yourself on the raw Orgone once at the cost of a perfectly good human, when you can invest in their survival and feed off their excess psychic energy their orgone field emits?