I heard some theory that Fire is Kaidou's weakness (kinda Irony for a Fire Breathing Dragon)
So just maybe Luffy will infuse Red Hawk with his COC
Which makes the Zoro vs King fight a suitable training for his fire-imbued slashes
i believe its not fire in of itself that does that thing but Ryou with red hawk... just like REd Roc was exclaimed to have that
new haki.
then again luffy has been using Acoa and it hasn't been doing anything significant even with gear 4 .. and luffy exclaims in disbelief that "the attacks should be working he's a human like us (low iq ) " so ryou wasn't doing crap to kaido itself but when luffy imbued ryou in red hawk... this is what he says
an interesting patter i bet we agree on.
shouldn't be a surprise if gear 5 has fire abilities
luffy is known to study his battles and evolve and devise things and this i bet is one instance where he tested his "theory"
then again if marco reaches the roof...
the trio (yamalolol, Warcooooo, WOOFY) would have all fire centric abilities