The Steel Release (鋼遁 Kōton) is an Advanced Chakra Natures that involves bending the users chakra into a physical shape around their body to enhance their own characteristics. The techniques once belonged to an unknown Shinobi clan who used it as a Kekkai Genkai. In the 3rd Naruto Movie, it is revealed that Hiruko used a technique to drain the Kekkai Genkai. It is unknown how any current users learned the techniques unless they are a branch from the clan.
There is also another form of Steel Release, where when using the Steel Release: Molecular Recomposition technique, the user can manipulate pre-existing metal with iron as one of the components and use the metal in a variety of ways. The Nekiogama clan consist of users who excel in this version of Steel Release and are often known as the Master Blacksmith Clan for their impeccable weapons and armor.
The most common form of the Steel Release was the ability to coat one's self in a somewhat malleable shell of metal that could be applied as an almost impenetrable armour or forged into weapons for various kinds of purposes. Numerous users of this version existed, among them Hiruko a missing-nin with the ability to steal the kekkei genkai of others.
Nikuya Seishin had an unusual variant of the Steel Release caused by the experimentation done to her by a member of the Kiri ANBU. Her entire form became malleable in the form of liquid metal which she could harden or soften at will essentially turning her into a living pool of metal. Through this version she could apply abilities similiar to the more common variant as well as techniques that were unique to her.
There is version of Steel Release usable by shinobi of the Kimza Chronicles series, mostly the Nekiogama clan. This version of Steel Release revolves around manipulating pre-existing metal and forming it into the needed shapes. Though this is mainly used by the Steel Release: Molecular Recomposition technique, many shinobi can manipulate the metal using other means.