The Forbidden Visual Jutsu

Sasuke places Danzo under genjutsu to kill him from behind, only to fall victim to the activation of a paralyzing curse mark placed on him earlier in the fight with Danzo insulting Itachi's act of sparing Sasuke while preparing to finish him off. But Sasuke's memories of Itachi allow him to cancel the curse and evolve his Susano'o as the fight soon recommences, Danzo's arm revealed to had been infused with the cells of Hashirama Senju by Orochimaru to use the Sharingan. At that time, Tobi deduces that Danzo is using the Uchiha Clan's forbidden jutsu Izanagi, which alters enough of the user's reality to avert death. Karin realizes the price for the jutsu is sacrificing a Sharingan for each use, realizing the jutsu's connection to the eyes on Danzo's right arm each permanently closing within 60 seconds of activation. The fierce fight between Sasuke and Danzo soon becomes one of stamina and will, Sasuke revealing he knew of Danzo's trick and that the latter only has a few Sharingan left to continue Izanagi.