Susanoo

Susanoo is a technique that creates a spiritual being resembling a yamabushi wielding the sacred, a mirror that's considered one of the three sacred treasures capable of reflecting all attacks, as a shield in its left hand, and in its right, the legendary , also known as the. The Totsuka no Tsurugi, commonly sheathed in a sake jar held by a third hand growing from Susanoo's right forearm, is an ethereal weapon with an enchanted blade capable of sealing anything it pierces in an eternal dream-like illusion, and is described as the perfect counter to Orochimaru's Kusanagi Sword. Like the Amaterasu, and Tsukuyomi, Susanoo is an ability of the Mangekyo Sharingan. Zetsu said that Susanoo's Totsuka Sword combined with the Yata mirror essentially makes Itachi invincible.
 * Debut (Manga): Chapter 391

The Sword itself can be presumed as an extension added to the technique as Zetsu mentions that 'Where ever he (Orochimaru) searched he could never find it.'.

Influence
Similar to other Mangekyo 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 Yata Mirror is one of the three Imperial Regalia of Japan, together with the Kusanagi Sword and the Yasanagi Jewel.