Susanoo

Susanoo is the third ability granted by the Mangekyō Sharingan, after the ability in both eyes have awakened. It creates a gigantic, spiritual humanoid being that surrounds and protects the user. 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's eyes and body are strained while using Susanoo because it consumes a large amount of their chakra. Sasuke described it as feeling pain in every cell in his body which only grew from prolonged use. Susanoo is formed through the materialization of the user's chakra and as such it may differ in appearance and colour between users.

Development
Susanoo goes through several development stages as users gain control of it. The various stages are best seen while Sasuke is learning how to use Susanoo, though Itachi can briefly be seen with both incomplete and complete forms when he first begins reforming Susanoo after Kirin hit it and when he runs out of chakra and nears death. In its earliest form, users can only manifest some of Susanoo's skeleton. Sasuke does this to produce a ribcage that he uses as a defense, though the bones can be broken, melted, or shattered. He also makes an arm to interact with his surroundings on one occasion. Because these skeletal structures do not entirely surround them, users can move around much easier.

As users gain additional control, musculature and skin begins to appear on the bones. It grows to its full size and the user is completely surrounded, eliminating the vulnerabilities of the skeletal form. Susanoo eventually develops into a "complete" form, with skin, armor and its final arsenal of weapons finally manifesting. It anchors the user to the ground at this stage, preventing opponents from forcibly moving them unless they can get through Susanoo's various layers. In its final form, this fully humanoid form is surrounded by a secondary layer of armor that causes Susanoo to resemble a yamabushi.

Itachi's version
Itachi's version is crimson coloured. In its left hand it wields the Yata Mirror as a shield. The mirror is endowed with all nature transformations, allowing it to change its own characteristics depending on the characteristics of the attack it receives, making the technique ineffective. In its right hand it wields the Sword of Totsuka. 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. Victims of the sword are trapped in a genjutsu-like "world of drunken dreams" for all eternity. Zetsu said that the Totsuka Sword combined with the Yata Mirror essentially makes Susanoo invincible, and it has thus been labelled the. It's seen that Itachi mastered his Susanoo and can change its form (from partially incomplete to final) at will.

Sasuke's version
Sasuke's version is purple coloured. While he is learning how to control it, Sasuke's Susanoo possesses a chakra blade for attack. Once he masters it, it gains a bow that doubles as a weapon and shield. Susanoo produces chakra arrows from its right hands, which can be fired at such speed that evading them is nearly impossible. The bow's design changes when his Susanoo gains a layer of armor.

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 composition compared to Itachi's Susanoo. It also has a more demonic appearance in contrast to Itachi's more human-like appearance; possessing horns, jagged teeth, and six fingers on each of its hands.

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 glimpsed as a shadowy figure in a genjutsu that Sasuke placed C under.
 * Sasuke's bow-wielding form of Susanoo bears a great resemblance to Raideen the Brave, one of a number of Yoshiyuki Tomino references in the series (another being the Gundam-derived names of Kakuzu's jutsu).
 * The Totsuka Sword wielded by Itachi's Susanoo is considered to be a "Sword of Kusanagi", although this has been popularly mistranslated as it being the perfect counter to the Sword of Kusanagi.
 * During the Sasuke vs. Itachi boss battle in Naruto Shippūden: Ultimate Ninja Storm 2, Susanoo doesn't appear around Itachi, but behind him, and it's more orange in colour than red from the anime. However, during his Awakening, Susanoo appears around him in a much smaller form.