Dragon Blood Slayer Magic

"Among Those Humans There Was One... Who Bathed In Too Much Dragon Blood... That "Man" Murdered Countless Dragons And Kept On Bathing In the Their Blood. Eventually His Skin Became Scales.. His Teeth Became Fangs.. And He Gradually Started To Look More and More Like a Dragon."

- Zirconis describing the Dark Dragon

Dragon's Blood Slayer Magic (勢力の竜: 殺意の魔法, Zeiryoku no Ryu: Satsui no Mahō, lit. "Power of a Dragons Blood: Ritual Killing Magi"): is a Lost form of Dragon Slayer Magic believed to be derived from the ritual used by Dragon's to create Dragon Slayer's. It is Blood Magic developed by Dragons, used to strengthen and empower human's, until they too undergo a ghastly transformation and to become Dragon's themselves.

History
Dragon's Blood Slayer Magic is old, perhaps one of the oldest forms of Dragon Slayer Magic, born in an era where war between the Dragons and humanity had only just begun. Humanity was on the brink of extinction, for against the sheer overwhelming might of the Dragon's what could a mere human accomplish? Magicians and sympathetic Dragon's eventually created a blood ritual, one that would grant a human the most coveted of all powers; the ability to slay a dragon. Thus Dragon Slayer's were born, but these first generation Slayers were just as monstrous as the very beings they waged war against. Like a Dragon they developed an insatiable appetite, and to their discovery, they gained the ability to greatly empower themselves by consuming and bathing in the blood of other living creatures. Once human, these Dragon Slayers eventually became nothing more than monsters, feeding on humans to gain incredible strength that would allow them to fight on equal ground against Dragons. Tyrants, dictators and cultists, these Dragon Slayers would eventually be transformed into Dragon's themselves, drunk on their power, eventually joining the legion's of Dragons who sought to rule over man. Eventually the method became more refined, allowing Dragon's to harness the power of the elements instead, and these Dragon Slayers unburdened by ravenous hunger maintained their minds and virtue in order to finally end the conflict.

Description
Dragon's Blood Slayer Magic is old magic, with roots predating the Dragon Civil War four-hundred years ago. It calls upon the most basic component of life, blood which is infused into the body of a human through a very complex ritual that allows the human to harness the power of a Dragon.