(Some) Powers of the Demon King:
Blood Master: Millen is capable of manipulating his own blood, and contains an unrealistically large amount of blood inside him. In truth, it would take him an entire year to bleed out normally. He can use this blood as a weapon, a shield, or for a variety of other uses.
God of Magic: Millen is capable of pulling off magic that is on the level of Gods, even if it might leave him vulnerable or drained. He could unleash a high level magic quite easily.
Unusual Charm: People tend to be attracted towards Millen...but it can also draw hostility towards him as well.
Void Linked: Millen has a connection to the void, and makes him able to use powers and abilities that are...something different. Not magic, not science, something else entirely.
Immortal: Millen cannot die, at least not easily.
Transformations: Millen can change his shape, bursting out of his current form into a new one. Has some...unfortunately...side effects though.
Gravity Manipulation: Millen was born with the ability to manipulate gravity.
Destruction/Degredation: Millen's powers can be used to absorb, destroy, and degrade matter as well as energy.
Sealed: While still powerful, some of his power has actually been sealed. His ability to change forms is limited to the normal transformations, and he cannot used the specialized combat form he created.
To be worked on later...
Demon King Blood:
-Awakens around the age of 10-12.
-Makes reproduction nearly impossible. This is because in addition to the powers affecting the ability to reproduce in the body, all Demon Kings will maintain an appearance of a child and prevents them from reaching the age where one would normally have a romantic relationship with. Additionally, the powers might overwhelm and kill the egg even if it initially works. Finally, Demon King's are known to be unnaturally drawn to trouble and chaos, which would make it difficult to get into a relationship in the first place. There are believed to be other factors as well, but those are big ones.
-Gives various Demon King abilities when born with it, and may still give some if one can survive being injected with it. These include Shadow Bending/Manipulation, Familiar and Monster Summoning/Creation/Manipulation, Blood Manipulation, and Degradation/Destruction Powers that work on a different system then magic and mana.
-Immortal. Once one Awakens, they stop aging completely.