Board Thread:Naruto Discussions/@comment-24847491-20140920090914/@comment-23887466-20140920210022

Well, Amaterasu is clearly Blaze Release. Just like Elveonora said Naruto doesn't gain a new nature after shape manipulating his wind Chakra. It just that the Blaze Release is always associated with the shape manipulation part of Kagutsuchi, instead of Amaterasu. But, they are both the highest level of fire release and that level is Blaze Release.