Susanoo

Susanoo is a technique that creates a spiritual humanoid being whose armor resembles a yamabushi, at least Itachi's version. The spirit is gigantic and surrounds and protects the user. It is the third 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. Like the the other techniques granted by the Mangekyō Sharingan, the user is strained while using Susanoo because they must act as a medium for the spirit, allowing it to consume their life force energy. Sasuke describes it as feeling pain in every cell in one's body, and while Itachi was close to death, it slowly deteriorated. Both Itachi and Sasuke are able to summon the spirit, though they differ in appearance. They both begin by forming a large skeleton with muscle tissue around the user. 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 Uchiha's version
Itachi's version gains another layer of armor and it wields the sacred as a shield in its left hand and the the legendary  in its right hand. The mirror is considered one of the three sacred treasures capable of reflecting all attacks, and the sword, which is 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, described as a perfect counter for his own Kusanagi 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 Itachi invincible, and has thus been labeled as the "Raging God of Battle".

Sasuke Uchiha's version
Initially, Sasuke is only able to partially manifest his version of Susanoo as a mere ribcage around himself for a strong defense or a hand capable of demolishing objects. He is also able to form the spirit with skeletal muscles for attacking, though not the entire creature. He is also able to combine the technique with Amaterasu to further increase his defensive power by making it impossible to touch Susanoo without being ignited. Sasuke's version has a much darker appearance, along with large horns and an additional finger on its hands. It wields a blade in its left hand capable of easily shattering stone pillars. After being enraged by Danzō, Sasuke is able to produce a fully manifested Susanoo, complete with flesh and armor. It has a bow on its left hand that doubles as a shield, and it can produce arrows from a third arm. The arrow is powerful enough that it can go straight through a thick tree and only have its trajectory changed slightly.

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.