Board Thread:Theories and Speculation/@comment-27082825-20150116155842/@comment-26023629-20150122173400

Well, the only other possibility under that theory is fire+wind+water (barring the existence of the two unknown two- part natures), which involves natures from the Land of Water, and with the heavy persecution of the Yukis (and presumably individuals with boil release) as well as the requirement of scorch release, which only can be found in the Land of Wind as far as we know, no one else could have made a three- part nature. As to how Mu came up with the idea: Mu's clan probably just tried breeding as many advanced nature users as they could find. Since the only other advanced nature besides those consisting of earth, wind and fire available in the area is explosion release, Mu possessing dust release occurred simply because there were only so many possibilities for advanced nature breeding within the limits of their region. From knowing his own ancestry, Mu was able to figure out how it worked and reproduce it in Onoki.

Also, as to that earlier theory, I think the difference in what I'm saying is that Mu and Onoki couldn't use any of the individual advanced natures in their blood, just the dust release. It's like how Kaguya had the ability to combine all 5 natures but didn't seem able to use any of the two or three- part natures we've seen. I feel that the every advanced nature is a "step" towards the ability to naturally create a TSB, and once you manage to "step" upward (from two natures at once to three natures at once), you can't use the stuff on the lower "steps" anymore.

Naruto being able to use two- part natures and TSBs is only because the advanced natures and TSBs come from separate sources: the tailed beast's abilities are separate from Naruto's.