Demon Kings are the children of Satan himself. They all lead their own armies of demons.
However, three Demon Kings; Mephisto, Azazel, and Amaimon, have since joined humanity.
It is also implied that most if not all of the Demon Kings have had encounters with the Archangels.
Demon Kings all have their own unique abilities but share each of the following abilities.
Flight - Demon Kings are able to fly.
Immortality - Demon Kings never age, get sick, or hunger.
Invulnerability - Demon Kings are immune to things that would kill most humans. This is shown when Astaroth was run over by a truck and he simply stated that it hurt.
Enhanced Strength - Demon Kings are incredible strong.
Invisibility - Demon Kings can't be seen unless someone is a Demon, angel, or human with a temptaint.
Possession - Demon Kings are able to possess human bodies.
Telekinesis - Demon Kings can move things without touching them.
Telepathy - Demon Kings all share a physic connection.
Teleportation - Most Demon Kings can teleport.
Regeneration - Most Demon Kings are able to heal themselves.
Enhanced Immunity - Demon Kings are immune to things like Holy Water, demonic wardings, exorcism, etc.
Killing - Demon Kings are able to kill angels.
Shapeshifting - Most Demon Kings are able to change their forms.
Perception - Demon Kings can perceive the true forms of angels.
Lucifer - The King of Light. Lucifer is the leader of the Illuminati and a steadfast supporter of Satan. He has repeatedly sent out demons to collect The Seven Seals, most likely with the intention to break them.
Samael - The King of Time. Also known as Mephisto Pheles, Samael turned against Satan long ago and joined the True Cross Order.
Azazel - The King with Spirits. Azazel also joined the True Cross Order. Shortly there after, he encountered the Archangel Raphael, who was stricken blind and banished to Assiah as punishment for disobeying God. Azazel then mocked Raphael thinking that in her state, she would never be able to defeat him. He was proven wrong, because while Raphael was blind, she was still an Archangel, and very unhappy with his mocking of her. Raphael won, and then crystallized the body he was possessing. At this point, Azazel's body is crystallized to the point where he can't so much as move a finger.
Egyn - The King of Water. Egyn is the only female member of the Demon Kings. She often goes to Assiah simply as a means of getting away from her childish brothers. She also has a strong sibling rivalry going on with her younger brother, Iblis.
Iblis - The King of Fire. Iblis has a strong sibling rivalry going on with his older sister, Egyn, because he hates the fact that she is so much stronger than him. Iblis is also jealous of Rin, because Rin has the blue flames which Iblis feels should belong to him, the King of Fire.
Beelzebub - The King of Insects. Beelzebub doesn't enjoy battling as much as his siblings. Still, when he feels threatened, he does transform into a full demon.
Amaimon - The King of Earth. Amaimon has also joined the True Cross Order. This is not out of loyalty to humanity though. It is because he is easily manipulated by Mephisto, King of Time.
Astaroth - The King of Rot. Astaroth is the most loyal son of Satan, as he continuously calls Rin "The Young Prince of Gehenna" while the rest of the Demon Kings have been willing to kill Rin at times.
Holy Fire - Holy Fire can burn Demon Kings.
Angel Weapons - Demon Kings are vulnerable to angelic blades. They can be killed by Angel swords whether it is an angel, demon, or human wielding them.
God - God can smite Demon Kings effortlessly.
Hearts and Tails - It has been said that nothing is more vulnerable than a Demons' tail and heart.
Each Other - One of the few things that can kill a Demon King is another Demon King.
Archangels - Archangels are the most powerful force in Heaven next to God Himself. They can kill Demon Kings, but higher level Demon Kings can over power Archangels.
Physical Trauma - Even though this won't kill the Demon King, enough physical damage can cause an Demons' human vessel to break down and force them to retreat to Gehenna.
Blue Flames - Demon Kings are affected by blue flames the same way they are with Holy Fire. They can be injured and even killed in serious cases.
- The Demon Kings mostly have names that are actually alternate names for Satan.
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