Its very likely some sort of genjutsu, possibly a Tsukiyomi. Sasuke just used two of his three techniques, Susanoo and Amaterasu and neither had any affect on Danzo. He may be trying the third technique now.
Another possibility is that Itachi is using a technique like Minato used to appear for a limited amount of time after his death. Sasuke really seems to be struggling against Danzo due to some unknown ability Danzo has been using to avoid every single one of Sasuke's attacks. Maybe Itachi knows about Danzo's ability and is going to tell Sasuke how to defeat it. Also he needs to come back to smack some sense into Sasuke.
I would personally hate for Itachi to come back. It would make his epic death meaningless and would kill that whole chapter of the manga. Also, Itachi transfered his eye techniques to Sasuke and some of his power to Naruto, so the new Itachi would have to be severely weakened. It would be a semi-powered, Amaterasu-less, Tsukiyomi-less and Susanoo-less Itachi. Also one of the reasons I love Naruto is because characters who die USUALLY don't come back. Its not DBZ where Goku dies, comes back, the earth explodes, is revived, everyone dies, but the Draganballs are used to revive everyone. Naruto actually has meaningful deaths and that is one of the best parts of the series.
Another possibility is that Itachi is using a technique like Minato used to appear for a limited amount of time after his death. Sasuke really seems to be struggling against Danzo due to some unknown ability Danzo has been using to avoid every single one of Sasuke's attacks. Maybe Itachi knows about Danzo's ability and is going to tell Sasuke how to defeat it. Also he needs to come back to smack some sense into Sasuke.
I would personally hate for Itachi to come back. It would make his epic death meaningless and would kill that whole chapter of the manga. Also, Itachi transfered his eye techniques to Sasuke and some of his power to Naruto, so the new Itachi would have to be severely weakened. It would be a semi-powered, Amaterasu-less, Tsukiyomi-less and Susanoo-less Itachi. Also one of the reasons I love Naruto is because characters who die USUALLY don't come back. Its not DBZ where Goku dies, comes back, the earth explodes, is revived, everyone dies, but the Draganballs are used to revive everyone. Naruto actually has meaningful deaths and that is one of the best parts of the series.