Mithril:

The Mithril (ミスリル)is the strongest, hardest mineral with the greatest magical conductivity (at a public level), from the other world, in the history of the eminence of shadows. This mineral is difficult to use and obtain, so only the members of the royal family of each country, at a public level, can acquire it, and the nobility in part, the members of the Cult of Diabolos, have also taken advantage of the mineral, to create its artifacts, from ancient times.