Susanoo

Susanoo is a technique that creates a spiritual humanoid being. 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 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 which resembles a yamabushi. 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 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 was only able to partially manifest Susanoo as a mere ribcage around himself for a strong defense. He proved to be able to further augment the ribcage version with Amaterasu in order to increase his defense by making it impossible for anyone to touch Susanoo without being ignited.

Later in his fight against the Kages and their bodyguards, he was able to form a spirit with skeletal muscles. In this form, Susanoo wielded a blade in its left hand, which was capable of easily shattering stone pillars. Once he forms the spiritual warrior, his Susanoo is portrayed with a dark shroud, along with large horns and an additional finger on its hands, which gives it a darker appearance when compared to Itachi's version.

After being enraged by Danzō, Sasuke is able to produce a fully manifested Susanoo, complete with flesh and armor. In this form, it has a bow on its left hand that doubles as a shield, and it can produce arrows from its right arms. Each arrow is quite powerful, as the trajectory of an arrow was changed slightly despite having gone through a thick tree. Danzou noted that it is very fast and thus is dangerously accurate and difficult to evade.

Sasuke's version has been shown to become more powerful whenever Sasuke experiences an intense feeling of hatred

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, its completed appearance was glimpsed as a shadowy figure in a genjutsu that Sasuke placed C under.