Hierro

is a defensive Arrancar technique.

Description
The user's Reiryoku condenses, creating steel-hard skin strong enough to block a Zanpakutō. This allows users to confront some of the sword-wielding Shinigami barehanded. In general, the strength of an individual's Hierro is proportional to the potency of their Reiryoku, though this is not a rule as Nnoitra Gilga has the hardest Hierro out of the Espada despite being ranked #5. Hierro is not absolute and opponents can adapt to cut through it, such as when 11th Division Captain Kenpachi Zaraki fought Nnoitra.

Trivia

 * In the English dub of the Bleach anime, Hierro was mistakenly identified as Cero when Ulquiorra Cifer spoke about Ichigo being able to effortlessly cut off Yammy Llargo's arm.