What if Crydo is a fraud Oni and implanted those horns to look like Elbaf Warriors
He even copied their Ikoku sovereignty move like Meme
I've suspected he's half Oni and hence his more humanoid resemblance compared to Oars and Oars Jr BUT I did theorise he was like what you suggested too. Less on a slander type thing, more a theory that Kaido idolised the Oni for their strength and size at least and thus always wanted to be like them.
So he puts on the fake horns and tries to LARP as them, wanting to be seen and included as one of them but with great rejection/resistance from them.
He had his horns when he was younger and we've not seen any sign from Yamatos they are fake too though...But we also have Maria, Ulti, Page, Sasaki I think with these horns so are they Oni too then? Would make sense I guess?
I rather Kaido was a real Oni but I suspected his storyline would be like Acnologia or even Itachi where he wiped out his own race for some reason. Or this would be King with the Lunarians instead lol.
Oda didn't show Kaidos people at Vodka kingdom/island or w/e, which I found very suspicious. Why hide that from us?
I have a headcanon, the freezing land of villains that Oars was from or died in, was Ringo or especially the Niflheim of OP, based at Elbaf especially and maybe Elbafs equivalent of Ringo too?
We had frozen giants at Punk Hazard, Saul a giant being frozen to "death" by Aokiji, Oars dying from freezing to death too, what else?
Also randomly I'm getting reminded of Majoras Mask and how Gorons were freezing there and their own hero froze to death lol. My brain is trying to weirdly associate/make a parallel here.