The Thirteen Circles is the collective name for 13 ancient and powerful demons, some of whom exist in Taborea to the current date. While a demon is any human who uses runes on themselves, the 13 have grown incredibly powerful over the course of their existence. The Circles are often connected with the "Demon Wars": a conflict of an unknown time period that occurred before the game's events.
Some of the constituents of the Circles have been encountered by the player and mentioned through the dialogue that they encounter.