However, Sasuke was not easy to deal with. Susanoo possessed both offense and defense, and even though Danzo could use a simplified version of Izanagi through the Sharingan on his right arm, relying on that forbidden technique alone made dealing with Sasuke's Susanoo rather difficult.
Izanagi was a forbidden technique of the Uchiha Clan. At the cost of sacrificing one Sharingan, the user recorded their own state. During the technique's effective period, all damage suffered by the user—including death—could be transformed into a dream, reverting the user to their initial recorded state.
Conversely, during that period, the damage the user inflicted on enemies would become real. This was a type of illusion—a highly advanced one—that could freely switch between dream and reality.
Danzo had mastered this technique, but he was not a member of the Uchiha Clan. Moreover, the prerequisite for using it was possessing a Sharingan.
Although Danzo was not an Uchiha, he possessed a vast personal power base. In his deal with Orochimaru, Danzo had him implant a large number of Hashirama Cells into his body. He had then implanted ten Sharingan in his right arm. This allowed him to use Izanagi for an extended period. Each sacrificed Sharingan gave Danzo one minute of Izanagi.
A Sharingan that had been used was basically as good as ruined, but Danzo had a large stockpile of Sharingan. Thus, ordinary Three Tomoe Sharingan were consumables to him, just like bullets.
Given Danzo's amount of Chakra, even after implanting Hashirama Cells, he had only ten "rounds" in reserve. Six had already been used, and he could only replenish them after returning to Konoha.
Danzo's original plan had been to first use the technique in his right arm to defeat Sasuke, then use the Sharingan of Uchiha Shisui in his right eye to