Board Thread:Versus Debates/@comment-142748-20150410212019/@comment-3965545-20150411235422

He was very sick the entire fight, Black Zetsu even said he was overall slower and his reflexes were slower compared to his normal self, then said Itachi should be much better, much stronger. It got fatal around the time he used Susanoo, his organs were failing hence the blood coughing, holding his heart like he had a heart attack and subsequently dying. He was also just about blind when Kirin was used.