Susanoo

Susanoo is the third technique/ability granted by the Mangekyō Sharingan, after Amaterasu and Tsukuyomi have been awakened. According to Madara Uchiha, for a Sharingan user to activate the Susanoo is a rarity.

This ability creates a giant spiritual humanoid being that surrounds the user and provides an impregnable defense and heightened offensive capabilities, giving the user incomparable powers in the middle of battle. However, like the other techniques granted by the Mangekyō Sharingan, the user is strained while using Susanoo due to it to consuming copious amounts of their chakra. Sasuke described it as feeling pain in every cell in his body, as the depletion of chakra likely places stress on the cells that partially produce chakra.

Susanoo is formed through the materialization of the user's chakra and as such it may differ in appearance between users. The emotional state of the user affects the appearance and weaponry of Susanoo. It begins by forming a large skeleton around the user, developing musculature and armor as the user releases more chakra to power the technique. Even in an imperfect state, the bones can act as armor for the user and it is capable of regenerating as long as the user has the energy to spare.

Itachi's version
Itachi's version was first shown in an incomplete skeletal form that managed to save Itachi from Sasuke's Kirin. It is able to turn into a humanoid being complete with skin, armor and a real face. It is further able to gain a layer of armor which resembles a yamabushi; in this final stage, it wields the sacred as a shield in its left hand and the legendary  in its right hand. The mirror is considered one of the three sacred treasures and is endowed with all nature transformations, it can change its own characteristics depending on the characteristics of the attack it receives, making the technique ineffective. The sword, a kind of Sword of Kusanagi also known as the, is sheathed in a sake jar held by a third hand growing from Susanoo's right forearm. It is an ethereal weapon with an enchanted blade capable of sealing anything it pierces in a "world of drunken dreams" for all eternity. Orochimaru sought the sword and Zetsu commented that he could never find it because it doesn't actually have a physical form. Zetsu also said that the Totsuka Sword combined with the Yata mirror essentially makes Susanoo invincible, and it has thus been labeled as the "Raging God of Battle".

Sasuke's version
When Sasuke is first seen using Susanoo, he is only able to manifest its ribcage. Though useful as a defense, the Fourth Raikage proves to be able to snap the ribs or even bypass them and attack Sasuke directly. As his battle with the Raikage and his allies progresses, Sasuke begins further developing Susanoo, combining the technique with Amaterasu and creating the technique the Shield of Amaterasu, effectively burning any person who gets in contact with Susanoo's skeleton with the black flames of Amaterasu. When Gaara joins in the fray, Sasuke further enhances Susanoo's form, the large skeleton gaining muscles which envelops him more completely and includes giving it horns on its head and three hands that have six fingers on them. At this stage, Susanoo can use its fists or a chakra blade to attack but can still act as a defense for Sasuke.

During his fight with Danzō Shimura, Sasuke is able to complete Susanoo, giving it the appearance of a demonic and evil-looking humanoid being and a bow that doubles as a shield. In this form, Susanoo can also produce chakra arrows from its right hands, which can travel at such speed that evading them is nearly impossible. While fighting Kakashi Hatake and driven by hate, Sasuke's Susanoo gains a layer of armor, similar to Itachi's, but with jagged sharp teeth around the hooded area and with a much darker and menacing appearance. The orb in its third hand also changes to a pitch-black color, while the bow in it's left hand also took on a different shape. This form was seen only briefly, though, as Sasuke's deteriorating eyesight caused it to fade away.

Sasuke's development of Susanoo is marked (albeit partially) by intense feelings of hatred; whenever angered by the words or actions of his opponents, Susanoo grows in power. His Susanoo is, accordingly, noted to be much darker in both in appearance and composition to Itachi's Susanoo. Bystanders have also noted how Sasuke's chakra seem to change and become "darker and colder" before and when he used this technique.

Influence

 * Similar to other Mangekyō Sharingan abilities, Susanoo was taken from Japanese mythology. Susanoo, the god of sea and storms, was the brother of Amaterasu and Tsukuyomi, with Susanoo born from Izanagi washing his nose.
 * The Totsuka Sword is the sword used by the god Susanoo to slay the eight-headed and eight-tailed snake, Yamata no Orochi, just like it was used by Itachi's Susanoo to defeat Orochimaru's.
 * The is one of the, together with the  and the Yasakani no Magatama (八尺瓊曲玉) Jewel necklace.
 * The is the sword used by Izanagi to kill his newborn son, Kagu-Tsuchi, after his birth burned his mother, Izanami, to death. From the blood of the Totsuka no Tsurugi, eight new Shinto gods were born.

Trivia

 * Prior to the completion of Sasuke's Susanoo, it was seen at least two times, once when Sasuke's "hatred" and chakra manifested as Susanoo before he attacked the samurai and the other time when its completed appearance was glimpsed as a shadowy figure in a genjutsu that Sasuke placed C under.
 * On Volume 51's front cover, Sasuke's Susanoo can be seen in the background and is shown to be blueish purple, in contrast to Itachi's being fiery red.