The Dragon King.

An existence which is considered as the absolute sovereign among all monsters and beasts. His might being, at least, on par with an adult Chosen, it was the biggest threat which the members of the race had to face.

If a Chosen wished to slaughter every monster in the continent, he wouldn't be able to do so as long as the Dragon King stays alive. If a Chosen could be considered as those who ruled over the divine among mortals, the Dragon King was the sole ruler over mana.

A dragon is originally a beast with a humongous amount of mana. 

Vampires who are those who hold the most mana among the member of the races usually have around 10-15 thousand mana by the time they reach adulthood. Whereas, an adult dragon had millions of mana. A certain legend says that their body could be considered as being fully made of mana which had been transformed into flesh and scales. However, no one had the luxury to perform enough research on a dragon's corpse to find out anything before being killed.

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And the ruler of these terrifying beasts, the Dragon King, held a power which no other dragon could go against.

The King's Crown.

Dragons, like nearly every being in this world, were limited. However, with the King's Crown, the Dragon King could surpass his limiter and his strength would evolve exponentially. The Crown was his symbol and source of absolute strength.

But it came down with a price. The Dragon King couldn't wear the Crown for more than 100 years. And afterward, he would be greatly weakened until his death. Thus, during their reign, Dragon Kings would usually try to groom a descendant to whom they could pass down the Crown, who happened to be in most cases their own son or daughter.

However, there was once a jet black Dragon King who didn't have any successor. For some unknown reason at that time he wasn't able to conceive a child with any woman. But his reign was coming to an end and he needed to select someone as the next Dragon King. Those who called themselves his friends tried to influence his judgment. The black Dragon King decided to leave his palace and roam around the world, before making any decisions.

Those who didn't know of his intentions thoughts that he wanted to select someone from the outside and were enraged about this idea. They then decided to follow the Dragon King in order to know which dragon he would select as his descendant.

However, the outcome of this selection was one which they would have never been able to guess.