Demon King

The Demon King (魔王, Maō) or King of Demons (魔族の王, Mazoku no Ō) is the title given to the leader of all demons. This role works as the counterpart of the "Heroes" title bearers and them destiny is linked with them.

Public View
The Demon King is the ruler of the Demon Nation and the strongest of them all. For the demons, they are the one responsible to give prosperity to the nation, but for the humans their existence is the greatest threat to the mankind. Most of the Demon Kings have a tendency to become violent and bloodthirsty with the time, starting wars.

Hidden Truth
Only know by few and recorded in even less documents, the origin of the power of the Demon King has been keep secret for a long time, since as the same way that the humanity's "heroes", the king of the demons is selected and receives their powers from a higher existence known as the "Black God". This being chooses at the Demon King to be his avatar and starts to corrupt him in order to make them personality more belligerent, bloodthirsty, and cruel, all in order to manipulate him to starts wars and presents him souls to feed in order to regain his lost power and with the time incarnates completely in the current Demon Kings body.

Selection
Similar to the heroes' mark, one candidate per every one of the 20 demon tribes receives a mark that indicates that they are able to become the next Demon King when the time comes for the current Demon King to die. So when the present Demon King pass away, then one of the candidates is automatically chosen and their mark changes into the mark of the Demon King.

Powers

 * Dark Energy Control - A way to slow down the advent of the Black God is by corrupting the offering given to him, nevertheless by doing this a side effect is that the corrupted beings develop a pseudo-immortality and cease to be members of their original races, becoming mere puppets if their egos are weak and monstrous warriors with their personalities wrapped if they are able to resist.
 * Demon Race Subordination - The standard ability that makes the Demon King are to emit "imperial commands" that obligate all the demons to obey him. Nevertheless this ability is not perfect, since only affect to those that hear the voice of the Demon King, even indirectly, and with the time some demons can develop resistance to that orders.
 * All Stats Correction - At the same way that heroes the Demon King gets corrections in them stats so he becomes stronger than the normal demons.
 * Level Limit Unlocked - At the same way that heroes the level limit of the Demon King gets unlocked and becomes infinite, making them able to keep becoming stronger the more enemies them defeat.

Known Demon Kings

 * Eve Reese (original timeline, Current Timeline: in position)
 * Hakuou (original timeline: predecessor of Eve, current timeline: deceases)
 * A Demon King from the Black Winged tribe (predecessor of Hakuou)

Trivia

 * The existence of a superior being that gives power to existences destined to oppose the heroes, Demon Kings, is a plot development also seem in "Shijou Saikyou Orc-san no Tanoshii Tanetsuke Harem Zukuri", another of the series of the author Rui Tsukiyo.