Just saying that there is totally friction underwater. And in the air too.
I know. I should have worded that better. What I meant was: You cannot generate flames via friction underwater. You'd have to evaporate the entire ocean.
Ultimately theres no way he generated those flames via friction. If that was the case then his Elephant Gatling would have been set ablaze as well seeing as how his fists were moving far faster than Red Hawk(you couldn't even see his hands and he wasn't even using G2) while in a bubble filled with oxygen which for obvious reasons would be far easier to accomplish than underwater(which isn't even possible).
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Strong will, that's whats Haki is about. Can you really see a such a petty character like Pearl have Haki? Fucking Pearl? So early in the series? Who wasn't even the strongest character after Don Krieg? Come on.
None of this matters. Anybody can learn Haki.
What I assume is Oda didn't had in mind CoA. Because for me, CoA was just something he came up with to counter the untouchable Logias, which by the time weren't introduced yet.
"For me" LOL. I like how you say that like your opinion actually matters in that regard. You're not the one who decides when the author comes up with an idea. Oda has clearly indicated that he had Haki in mind since chapter 1. Your silly opinion on it doesn't matter.
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Marigold used a match, btw. flies away
Actually it was a lighter if I recall correctly. But I still believe the reason for her Salamander technique was Haki. The reason being because Sanji another Busoshoku Haki user used to have to spin in order to set himself on fire. Now after his training he no longer needs to spin or use friction which indicates that with further mastery certain characters no longer need to kick-start their flames with a match or friction. The way they used their Busoshoku Haki suggests that it must have some affinity towards flames because when you look at when they set themselves on fire they themselves don't feel a thing yet anyone else gets burned from the flames.
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There are special cases where they are born with it, I think that was Otohime's case too.
There are no special cases when it comes to who can learn Haki. Everyone has it. Anyone can learn it. You don't have to be special or significantly strong in order to have the ability. Excluding Haoshoku of course.