Demon King

The is the king of the Demon Clan. He is the one who handpicked the Ten Commandments and granted them their Commandments.

Appearance
Though the Demon King's true appearance has yet to be seen, he appears before Meliodas as a massive shadow made of darkness.

Personality
Not much of his personality is known yet. He seems to put power and evil above all else, chastising Meliodas for throwing away his former life just for the sake of one woman.

3,000 years ago
The Demon King fought against Meliodas who was accompanied by Gloxinia and Drole prior to their eventual defection to the Demon Clan and was defeated by them. At one point he cursed Meliodas with immortality, causing him to be unable to die regardless of the method used to kill him.

Battle for Liones arc
After Meliodas's fight with the Ten Commandments, the Demon King greets him in Purgatory. He admits to having been keeping an eye on the captain of the Seven Deadly Sins throughout and muses that even Meliodas was unable to do anything other than wait for death when caught by the Commandments of Piety and Love. When Meliodas counters that he is now free from the Commandments' bindings thanks to his curse, the Demon King agrees but mentions that he can feel Meliodas' quivering. Entertaining Meliodas' bluffs, he expresses anger towards the certain woman who had changed Meliodas and then informs him that though he was left in a greatly weakened state, the curse he casted on the Dragon's Sin of Wrath would allow him to feed on his emotions every time he dies, allowing the Demon King to regain his lost power and at the same time reverting his traitorous son back to the state he was three thousand years ago. He is then attacked by an outraged Meliodas.

Abilities and Equipment
The Demon King is extremely skilled with blessings and curses, having been the one who created the Commandments that the Ten Commandments wield. He is also responsible for the seemingly unbreakable curse on Meliodas that has lasted for at least three thousand years.

He is also incredibly powerful, enough to be the ruler of the entire Demon Clan. All three of his sons inherited his strength, with their individual power levels amongst the highest of all known characters.

Abilities

 * The Demon King is capable of bestowing a Commandment on those he deems suitable. These Commandments deliver a unique curse to whomever breaks a rule specific to each Commandment. This power is absolute; it cannot be opposed even by its wielder. The curses will only be lifted if the victim defeats its wielder or at the victim's death. Notably, these curse are not magical in origin, activating even when they're holders are drained of magic.
 * The curse's effect is unknown, though running away from him will trigger its effect. It was held by Calmadios.
 * Those who show faithlessness in the holder's presence will have their eyes set ablaze. It was held by Melascula.
 * Those who stand before the Commandment holder with hatred in their hearts will be rendered powerless to harm or inflict damage on anyone else. It is held by Estarossa.
 * Any who kills in the holder's presence will have their own time stolen from them, causing the victim to age rapidly and die. It is held by Grayroad.
 * The curse and its activation are unknown. It is held by Drole.
 * Any who turn their back to the Commandment's holder are treated as committing an act of treachery, and are cursed into serving the Demon King, and by extension the holder who is acting as the Demon King's representative. It is held by Zeldris.
 * The curse and its activation are unknown. It is held by Derieri.
 * The curse and its activation are unknown. It is held by Gloxinia.
 * The curse and its activation are unknown. It is held by Monspeet.
 * Though the Commandment's activation is unknown, those inflicted by its curse will lose their memories, feelings, and entire sense of self. It was once held by Gowther, but was later passed on to Fraudrin upon Gowther's disappearance.
 * This Commandment determines that any who tell a lie in the holder's presence will be turned to stone. However, only those who are aware that they are lying will be affected. It is held by Galand.
 * Immortality Curse: A curse that revives the victim without fail regardless of the means of death, including suicide or getting killed, no matter how many times they die. It additionally prevents the victim from dying of old age. In exchange for the infinite number of revivals, the victim's emotions are slowly drained to nourish the King. The conditions to dispel it are largely unknown.

Meliodas
He and Meliodas now have an antagonistic relationship, though how it was before Meliodas betrayed the Demon Clan is unknown. He lightly mocks his defeat and descent to Purgatory, yet he seems to revel at the idea of bringing his traitorous son back into the fold, with force, if necessary.

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