I’ve read so many comments about this “big punch” that Luffy’s using to clash with Kaido, saying that it cannot be the one to end the fight, or that it would be disappointing if it did because Oda said it shouldn’t. I kinda disagree, and for me to explain why, we need to go back to the original quote.
The quote is from 2016. Oda’s words were:
“When Kaidou appeared for the first time, I said that Luffy can’t defeat such a strong character yet. And I’m yet to know how Luffy would defeat Kaidou. Probably my audience will not be satisfied if the reason for defeating Kaidou is just because Luffy’s punch is so strong. Luffy and I have to find a solution somehow.”
So, the problem was that Luffy was too weak to defeat Kaido at the time. Luffy’s punch being so strong wouldn’t be a satisfying way to beat Kaido according to Oda, which is true, but that doesn’t mean that Luffy’s final blow to Kaido wouldn’t be a punch.
In order to defeat Kaido after losing against him for the first time (something that happened 2 years after the quote, in 2016), Luffy first had to learn advanced Armement Haki. With it, his fist, head and even his sandals became able to deliver his Haki into Kaido’s body, allowing him to finally damage the Yonko.
He later used the same concept that allowed him to channel said Haki, to channel his Conqueror’s Haki as well. All the pieces of the puzzle were there. He could already channel his Conqueror’s Haki to specific people thanks to Rayleigh’s teachings. So with his newly acquired ability to manipulate Haki at a smaller more focused scale, all he needed was to notice that Kaido wasn’t just using Armament Haki to attack him, but Conqueror’s Haki as well.
Luffy had to dodge using advanced Observation Haki, manage his energy better than ever before, and bounce back from defeat multiple times, just to be able to stay in the battle long enough to awaken his devil fruit.
And what did this Awakening give him? It gave him the ability push himself more than ever before, the ability to wrap himself around Kaido’s attacks to reduce the damage he took, the ability to manipulate all of his surroundings and use it to his advantage, and the ability to hurt Kaido even more by digging physically into his body (pre-awakening, only his Haki dug into Kaido’s body).
Now, in this final clash, it’s his ability to channel his Haki outside his body that’s keeping his (probably) final punch from being disintegrated. Yes, the very first thing that Luffy deliberately sought to learn is now proving to be so crucial in this clash.
If his final attack was a kick or a headbutt, would things be better or even different? Of course not!
If Luffy wins the fight with this punch, or another punch for that matter, he wouldn’t be winning because he punches hard, he would be winning because of everything else that I mentioned. If you take away one of those elements, he would lose. Oda made sure that almost everything Luffy did to get from being one-shot by Kaido, to where he is now, had nothing to do with being able to punch physically harder. In fact, take away Oda’s statement, and I’m willing to wager most people wouldn’t think of the attack being a punch or a kick.
If you’re a Hajime no Ippo fan, maybe this example would explain what I mean. Kamogawa defeated Anderson by punching hard, hard enough to push his enemy’s ribs into his lungs. But did Ippo defeat Sawamura because his punch was hard? Nope, it was because he learned to counter Sawamura’s Dempsey Roll counter. Of course the final blow was a punch; the man is a boxer! But his punch being harder was not the key to his victory.