I've see this fight quite a few times but I never understood if Danzo used Shisui's eye?
When Sasuke pierces Karin & Danzo with his extended Chidori, did Danzo use his last Sharingan (Shisui's eye) or he didn't get a chance to use as Sasuke's attack was unexpected/surprised?
Danzo was using Shisui's eye. Check out the episode with the 5 Kage summit where he is influencing the other Kages to vote for him as the leader of the summit.
Danzo knew about the power of Shisui's sharingan, but was also aware about its awakening period, i.e Danzo could not always use Shisui's sharingan due to the immense power of the jutsu (Kotoamatsukami) that Danzo was using.
Also, that might be the reason he took karin as hostage.
The whole point why Danzo infused himself with Hashirama's cells was so he could manage the many sharingan he stole and to lower the cooldown time on Shisui's Koto.
Sasuke killed him before Danzo could use it on him in their fight, Tobi clearly states it.
Danzo underestimated Sasuke and was planning on using Koto if he fought Tobi after Sasuke. Sasuke placed Danzo in a simple Genjutsu and died before using it.
