Just something I've noticed. He appeared after Ace and Blackbeard's fight, after the Straw Hats were separated, after Marineford.
I think there was some narration at the end of Skypiea and Thriller Bark. I'm not too sure.
Oh, I see, you meant the narration boxes. That wasn't what I was talking about, or rather that's only a small piece of it.
I mean the narration, how the story is told. From what I can tell, when characters have flashbacks, we're seeing what literally happens, not a characters memories that would naturally be colored and morphed by time and experienced, or even their present, which would have the perspective skewed according to a character's bias'. We see perspectives of past characters of the flashbacks that the character that is supposedly remembering them couldn't possibly be aware of. And when the narration boxes come up, they usually are just reporting facts with neutrality. "This is character X, bounty Y, on Z island" or "Whitebeard took 64 stab wounds, 134 gunshots..." and so on. Chopper's entire flashback takes place in the split second of Luffy punching out a guy, literally faster than thought of that detail can be recollected, implying time is literally put on pause, rather than the character recollecting the event as a natural part of the story.
So what I'm saying is that the narration of OP isn't taking place behind any particular character and seems to be giving us the literal truth of what happens. The "Haki can only be seen by those who know Haki" theory would only make perfect sense if we were seeing the story of OP from Luffy's perspective, or even a limited third person perspective. Something that is meant to influence the truth of what we are seeing. But if it's a omniscient third person narration, which, as the name suggest, then the narration would be fully aware of Haki from chapter 1 and have no real mechanism to hide it, since as the name implies, it's already aware of it, even if none of the characters are.