Earth Release: Earth Spear

The user flows earth-nature chakra throughout all (or specific) parts of their body, causing it to become noticeably darker and sustain an increased carbon density until the flow of chakra stops. This increases their defensive power to its utmost limits by making the skin and flesh as hard as diamond. Furthermore, the destructive power of physical attacks is greatly increased by the technique, at the cost of the effected areas becoming rigid and unmoving when active. The benefits make this a great all-purpose technique, as movement can be retained by leaving joints unaffected or only partially hardened.

The amount of techniques that can break through the areas fully hardened by the Earth Spear are close to zero, excluding its undeniable weak point: Lightning Release ninjutsu and Raiton chakra in general. These may be partially reduced in effectiveness after passing through the technique, however. (Raikiri made a much smaller hole then normal, when going through this.) In the anime, Kakuzu used this technique through the use of his earth-element mask. This mask gave him the extremely high earth affinity that is essential to even attempt the technique.

Kakuzu demonstrated precise chakra movement, to use this to cover himself partially (i.e. his hand and lower arm, and the side of his head) without using handsigns. This gave him a significant tactical advantage against ambushes and showed mastery of the technique.

The Earth Spear was most likely developed through examination and study of the Steel Release bloodline, later on aquired through unknown means by Kakuzu in his travels bounty hunting. The snake seal used in the technique appears to allow easier focus and control of the elemental chakra released through the body, rather then simply molding it into a jutsu. There are no other confirmed users of this technique, although as a chakra-flow skill it would have had to be taught. The question on if said teacher was allowed to survive afterwards is up for debate.

Trivia

 * Like the rest of Kakuzu's techniques, the name of this technique comes from the legendary mecha anime . The name Domu was taken from the Gundam MS-09 . The name was given kanji to create the name of this technique.
 * This technique's attribute of darkening of skin colour as a result of hardening is similar to Hiruko's Steel Release technique.