My theory is that Itachi Uchiha gave him the ability when he was under Tsukuyomi, and that is why his resembles a pseudo-version of Itachi's. Remember, it's established that Itachi Uchiha can give other people *powers* which was seen when one of his black crow's went up Naruto's throat, and Itachi said he hoped he wouldn't use it on Sasuke.
What do y'all think?
What do y'all think?