Board Thread:Fourth Databook/@comment-4366149-20141122004623/@comment-1512913-20141203150150

I say it's no doujutsu because Amaterasu isn't the only way to "release" the black flames. Chapter 698, Sasuke's Rinnegan eye is defunct, he activates his Mangekyou and uses just "Kagutsuchi", there was no "Amaterasu" prior to that, meaning the source of the black flames was his hand, no differently than Chidori is used.