Yasaka Magatama

Using the complete form of Susanoo, the user is able to create the Yasaka Magatama between two of its arms, consisting from a number of tomoe bound together through their respective centres by a thread of chakra. Due to this structure, the tools then act in a similar manner to that of a shuriken when thrown by Susanoo, rapidly spinning towards the intended target.

In Itachi's demonstration, three tomoe were bound together by a single circular thread, after being created by the right arms of his Susanoo. The entirety was then thrown towards the target as a single projectile, which Itachi asserts to be his strongest long-range technique.

In Madara's demonstration, a considerable number of tomoe were strung out between two of his Susanoo's hands, using an interconnecting thread. When thrown, the entirety detached from one another, with each individual tomoe becoming a separate projectile instead.

Influence
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Trivia

 * The shape of Itachi's Yasaka Magatama, three tomoe bound together by a single circular line, is reminiscent of the completed form of the Sharingan as well as the Cursed Seal of Heaven.