Steel Release

The is a combined nature transformation  kekkei genkai. It is unknown what elements this nature entails.

Forms

 * In Gaara Hiden, Metoro Konjiki from Ishigakure can use the nature to produce steel weapons.
 * In Naruto Shippūden the Movie: The Will of Fire, Hiruko, who stole this nature from an unknown shinobi by using his Chimera Technique, turns his body into steel, making it virtually indestructible.

Trivia

 * In Sasuke Shinden, a member of the Purple Moon Religion is able to create steel weapons from the surroundings. Sasuke Uchiha describes it as a powerful ability that he's never seen before, but beyond that the ability isn't explained.
 * In Naruto Mobile, Steel Release is implied to be created by simultaneously combining the Earth and Lightning natures.