@Bogard Maybe Oda wants to trick us and therefore put that "CoC sphere" clash in there. Cause in the panels right after the clash it looks like they locked eyes in a standstill. Those stripes are in front of them then. So their weapons probably touched afterwards. He pretty much let us fans guessing, which turns into such" Was that advCoA+CoC? " discussions.
Or he just put it in because he pretty much has to in those - over the top- clash panels.
And that tail might be the result of a huge amount of hardened up haki, that would otherwise wildly flow around the weapon. It's there to "sharpen" or condense the huge amount of haki they gathered via advCoA. In that famous swordsman quote it is also said that they ".. Can chose to not to cut anything..". Perhaps those huge amounts of haki in their natural Form turn more into a blast like attack rather than into a cut.
Similar to the attack that he pulled out against Oden in that chapter, cause he prolly did not intend to kill him. So you can chose to either have a raw blunt force swing (with higher AoE) or a cutting attack. Transfered onto a punch, you might either be able to chose between the big Shockwave tech or perhaps a black haki bubble around your fist that emits the same "tail"/stripes and packs more of a punch but on a smaller AoE.
This would be supported by the fact that those stripes are later seen (if I'm not mistaken) when Oden carves in Roger's words into that Porneglyph. So Oden was seemingly able to use that "tech" aswell.
Which would also make room for a potential lvl which is even above that, where Roger then for real mixes in advCoC and Whitebeard turns on his gura gura no mi. Which got off paneled and which is the stuff that made Oden admit, that Roger, just like Shirohige, was far out of his league aswell.
The wano war will probably clear this up tho.
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@comrade I start to think that the Mera Mera no mi might turn out to be a S class df in combination with those adv. Haki types.
You have incredible evasiveness (With FS, mimicking Kata's mochi defense, perhaps even better, like Smoker) while also very fast in Cqc, flight and the casual power of a hiken that you can additionally put into such swings or attacks.
In general I agree with you. Zoans definitely start to become more beneficial.