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's version
Itachi's version was first shown in a skeletal form that, despite being incomplete, managed to save Itachi from Sasuke's Kirin. It soon forms into a complete armored form that resembles a traditional samurai but is able to gain 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 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 developing additional skeletal structures and musculature for Susanoo, 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 further Susanoo's development, giving it the appearance of a samurai but with a more demonic and evil-looking appearance 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 another 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. This form was seen only briefly, though, as Sasuke's deteriorating eyesight caused it to fade away.

Sasuke's development of Susanoo is marked 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 chakras seem to change and become "darker and colder" when he uses 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, its completed appearance was glimpsed as a shadowy figure in a genjutsu that Sasuke placed C under.