Of the three irreplaceable materials, Angel had only heard of the Undying Burning Bone of the Black-Gold Nightmare.
The Black-Gold Nightmare was a peculiar Demonic Beast from the Abyss. Sanders had once fused with the Black-Gold Nightmare's bloodline, and even the Nightmare in the original spell he had developed, Nightmare Substitute, referred to the Black-Gold Nightmare.
The Undying Burning Bone of a Black-Gold Nightmare was also a precious magical material to alchemists. There should have been some stock of it in the Wizarding World.
But he had no way of leaving the Abyss now, so finding such a magical material would be difficult.
Aside from the Undying Burning Bone of the Black-Gold Nightmare, Angel had never heard of the other two materials. However, that senior had written down their origins.
Earth-Vein Fire Rock that had accumulated for over a thousand years—when Angel first saw the name Fire Rock, he had assumed it was some kind of ore. But after reading more carefully, he discovered that it was actually a semi-elemental lifeform in a benighted state, on the verge of awakening its spirit. It was also the favorite food of Fire-Passing Demons.
Such semi-elemental lifeforms generally slept beneath lava.
With Angel's current physical resistance to high temperatures, he could not endure a journey beneath the lava.
So this was not an easy material to find either.
Yet among these three materials, the hardest to find—and the most important—was the White-Ash Fire Solvent brewed with Hellfire. Calling it hard to find was not quite right, because the difficult part was not the White Ash that came after, but the Hellfire at the beginning.
From what Angel currently knew, the only beings capable of releasing Hellfire were... Fire-Passing Demons.
In other words, to refine White-Ash Fire Solvent, he needed a Fire-Passing Demon to