A creation of Yuuki Terumi which caused great chaos and calamity, the Black Beast is a monstrous being that is made up of the substances known as Azure and Seithr. It is featured in Genesis Catastrophe.
The Black Beast is a bestial creature born to cause torment and pain, created to orchestrate the First War of Ars Magus by Yuuki Terumi. It was the main opponent of all humanity during the decade-long war that revolved around it. Its only instinct was to main and kill anything that stood in its path of destruction. Its presence in the world resulted in the world being completely veiled in a lethal and toxic substance humanity named Seithr, in order to operate at full efficiency. During the First War, a warrior participating during the war, Bloodedge, helped keep the Black Beast dormant for a year while the Six Heroes, a group now renowned for saving the whole of humanity, taught to humanity the power of Ars Magus. Ten years after it first appeared, the Six Heroes had banded the remnants of humanity together against the Black Beast and managed to slay it once and for all. However, as it died, it let the world be completely drown in the Seithr that circulated in its body.
The Black Beast's mere existence and its actions left a long-lasting impact on the world; in order to adapt to the inhospitable environment, humanity created the Beastkin which were more resistant to the Seithr that flooded the world, but it was only a slight measure. In order to live in the now poisoned world, humanity built structures on top of mountains which were high up into the atmosphere called Hierarchical Cities. Ars Magus became common place in the world and its culture, as the government known as the Novus Orbis Librarium took over as central controller of the world.
Due to the otherwise lack of information surrounding the war, much of what the Black Beast did and could do were largely forgotten by the 27th Century.