User blog comment:Pauldin91/Haoshoku Haki Master/@comment-24850639-20161011205633

I concur that the series hasn't taught us much about haki, but just because Kairoseki and haki both impact DF abilities doesn't mean that there's a connection between the two. Until we have more solid info on both, best to leave that one alone. Now as far as haki is concerned, as of right now we just have what we learned from Rayleigh as our only real concrete knowledge, and what we've observed with our own eyes. Mihawk didn't reveal anything new about it from what we saw of him training Zoro, and I'm sure Ivankov played some kind of role in teaching it to Sanji, but we've seen absolutely nothing of that. Based on what Rayleigh said, Kenbunshoku and Busoshoku are inherent, dormant abilities in all people. They are developed through regular training, just as we saw with Luffy. Haoshoku however, is an ability that one must specifically be born with you simply either have it, or you don't. Garp said something about Luffy "inheriting" it during Marineford, so perhaps there's some genetics involved, but we haven't seen Garp, Dragon, or Roger use it as of yet. Most importantly though, Rayleigh said that it CAN'T be improved through training. In order to develop one's Haoshoku, a person must develop themselves first and foremost. We don't quite know what this means either, but given the trials and experiences that Luffy goes through over the course of the series, it should be safe to believe that his Haoshoku will naturally get better from Luffy just being Luffy.

On another note, you raise a good point about combination. For the most part its safe to assume that Shanks doesn't have a DF, so he HAS to have some kind of capability that makes him able to stand on equal footing with the other Yonko. Logically one would assume this to be his haki, but from what we've seen so far, haki as is shouldn't put someone on that level. Kenbunshoku can be rendered ineffective by unpredictable fighting styles, Busoshoku can simply be trumped by stronger Busoshoku, and Haoshoku seems to be limited to weak-willed opponents, which should be an afterthought in the New World. I'm in the camp that believes haki types can be combined in some kind of way, and that the truly strong people of the world have found innovative ways to combine them that opens up an entirely new world of power. People like Rayleigh and Mihawk without DFs have to have something that gives them an edge, otherwise they would have earned their titles.