He had done it.
An Su was deeply respectful, this was the most powerful, most forbidden Summoning Magic since the Era of Chaos.
"Black Blood," also known as Magic Oil.
Bards sang of it; Magic Oil was claimed to be composed of the piled corpses of mythic creatures from ancient times, countless beings lay dormant within the earth, millennia of resentment and souls merging into the corpses, from which the black blood eventually flowed from deep within the crust.
Black blood was the cornerstone that allowed the Era of Chaos to thrive robustly, being the raw material for the magic industry of Nether for thirty thousand years, essential for both the alchemist's alchemical matrix and the Disaster Apostle's Stitched Life.
Sages too had prophesized that if the black blood were to be sacrificed, freedom's Radiance would descend.