Fiends are evil spirits. Little is known about them for they have been imprisoned for thousands of years in Gorsus. While trying to save Cameron, Baldewin had to choose between releasing an Archdemon or a thousand fiends. He chose the latter, setting all thousand free. A member of the Hernessia Guard found a note in a cultist's house stating that the release of the fiends at the expanse of the Archdemon was planned all along by a Black Heart spirt. Accoriding to the Tha'hune a fiend can only be killed by burning his head. If this ritual is not executed the fiend will simply regenerate or respawn at a later moment in time.
In later events the fiend Azor forms a group togheter with lesser fiends and starts a conspiracy of an huge magnitude in order gain total control of the continent. Azor does so by expoiting the king's absence and starts manipulating the young prince Edard. Under Azor's influence Edard claims the throne and starts infading nearby towns and village's. He also tries to conquer the white tower, but does not succeed in capturing any place of significance due to Kamala's interference. Some of the lesser fiends succeed in taking control over tribes and other key figures by exploiting their fears, primal needs & cravings for power and magic. Kudzu a crime lord in Borndahl is manipulated by Ru "The Let'ter" and starts extorting the weak. Tribes like the Gooka's and the Idocas tribe of Goatmen are also heavily manipulated. The Gooka's became so dependent on the fiends magic and power that the Tha'hune could not save them.