Board Thread:Theories and Speculation/@comment-26061639-20150131220909/@comment-4912646-20150412060438

Just want to point out that while the Ten-Tails (and presumably Kaguya) manipulate pure natural energy, they are not considered users of senjutsu, at least according to the databook (which is questionable, of course). My point being that Ten-Tails being one with nature and using Wood Release doesn't necessarily have any correlation with Hashirama's Sage Mode. I agree that his Sage Mode likely wasn't taught to him by animals though, which is why his takes on a more generic look than the other users.

Actually, since the appearances of other users' Sage Mode are based on their summons, perhaps Hashirama's has something to do with the Rashōmon (or whoever/whatever created the gates).