Noblesse Oblige.

Izanagi has the capability to make anything an illusion and make any illusion real. It blurs the line between reality and illusion, thus making it the most powerful genjutsu ever. The after effect of using Izanagi is that the user's eyes will never open again. Danzo circumvents this by having 11 different Sharingans embedded within himself. Thus if needed, he can use this technique 11 times. Since Izanagi can hypothetically make some insanely powerful offensive illusion real, it is very dangerous to the opponent. As a result, Sasuke pulls out all his techniques to force Danzo to use his Izanagi defensively. In addition, it seems that the Sharingans on Danzo's arm does not give him any nerve response or visual feedback, so he does not know when one of them has been closed. Consequently, Danzo has to keep checking how many Sharingans he has left to use, and Sasuke took advantage of this by casting a genjutsu on Danzo to make him think he had one more Sharingan than he actually did. When Sasuke and Danzo lunged at each other with their swords Danzo tried to activate Izanagi with his non existant Sharingan. Since it didn't work, he got critically injured from Sasuke's sword. Both Madara and Sasuke comments how a real holder of Sharingan is stronger than someone who borrowed the eyes. Karin quickly heals Sasuke, but Danzo gets up once more after severing his out-of-control Shodai cells. He reveals Shisui's Sharingan to Sasuke. It seems there's something special about Shisui's Sharingan which stops Danzo from throwing it away as a defensive Izanagi. He hinted that it might be a powerful genjutsu, but I don't know what could be more powerful than Tsukiyomi and Izanagi, which manipulates time and space respectively with illusion. Danzo wasn't sure whether to use the Sharingan on Sasuke or Madara, so he takes Karin hostage to buy time. However, Sasuke is merciless as he stabs through Karin with a Chidori blade to pierce Danzo's heart. Karin dies immediately but Danzo as a last attempts activates a sealing jutsu that tries to seal all those around him to his dying body. However, Madara recognized it and both he and Sasuke are able to avoid the jutsu. Moments before Danzo's death, we learn from a flashback that the reason for everything Danzo has done is to measure himself against the Third. Prior to Danzo's activation of his final jutsu, Madara said he was going to take Shisui's eye; however, now that Danzo has sealed his body it is not clear whether Madara can still do so. On another note, Sakura and her group is closing in on Sasuke while Kakashi is close behind in his attempt to stop the encounter.