Tamahagane

Domus Steel (ドムス鉄鋼, Domusu Tekkō) is an incredibly precious natural ore that is invaluable to mages, as well as being one of the rarest metal ore's in Earth Land.

Trivia

 * Domus Steel is based on the real life ore known as Damascus Steel, a type of metal that in modern times has yet to be replicated due to modern scientists, metal workers, and blacksmiths not knowing the exact metal composition, making it one of the most perplexing innovations of the ancient world. In ancient times though Damascus Steel was one the hardest metals, and thus was one of the most sought after materials in the crafting of weapons.