Mareth

Mareth is the world in which the story of Corruption of Champions takes place. It is an entirely different world to that from which the Player Character comes, and the game opens with them being transported there via an interplanar portal. Currently, little about the world has been actually written up, in the manner of the various Codexes; instead, what details about the setting are known have been revealed by Fenoxo during conversations on his special Fenchat.

Approximately two hundred years before the present day of the setting, Mareth was empty of sentient life; while at least one god-like entity, Marae was present, the only life-forms were animals. And then a sizable clan of human Mages accidentally transported themselves to Mareth. Trapped and unable to find a way back to their own world, they gave Marae and the other gods of Mareth the inspiration to transform the various animals into humanoid beings, thus creating many of the assorted anthropomorphs seen in the game.

While it's currently unclear whether or not the portals are in some way tied to the clan of Mages, the many portals on Mareth did contribute to its diverse population by bringing in other races to the planet.

A quirk of Mareth's nature makes it extremely easy to get to this world, but almost impossible to leave it. Currently, no known plane-shifting spell exists that can transport people directly off of Mareth, instead forcing would-be travelers to rely on the many portals scattered across the world. Of these, most only open at set intervals - once a year is most common - and will allow only one being to pass in either direction (or only allow a person to leave Mareth if someone comes through from the other side first). These are referred to as "stable portals". Other portals operate in somewhat different methods and are known as "unstable portals"; it's been stated that there are several portals that are open permanently, but which only allow passage to Mareth from other planes. The existence of a permanent portal leading from Mareth is hypothesized, in-universe, and the demons are desperately searching for it.

The demons first appeared in Mareth some thirty years before the start of the game. Despite decades living in Mareth, the descendents of the first mage clan never lost faith in the idea of someday returning to their own world. Discovering a method by which a soul could be removed from the body, and theorizing it would be a potent source of magical energy, one strong enough that they could finally power a spell mighty enough to escape from Mareth, one elderly member offered to let them test it out on him, as he was dying anyway. He became the first demon. Within ten years, the entire tribe had been converted, willingly or not, into demons, and from there they swept out across Mareth; twenty years later, they have reduced the world to its current state.