At this point, I think a lot of people agree that at some point in the battle, Kaido’s scar will be reopened. However, the one who opens the scar won’t be Luffy or Zoro.
During chapter 992, the Scabbards all attacked Kaido’s scar with the same technique Oden used to open it 20 years prior.
However, as we saw, Kaido mocked the Scabbards for not being able to reopen the scar, and went on to defeat them all.
However, what if that final attack DID do damage?
More specifically, what if that final attack did just enough damage that, if someone else were to push Kaido to his limits, the scar would open on it’s own?
My theory is that the final attack done by the Scabbards in 992 will end up being a Chekhov’s Gun that will take effect once Kaido accumulates enough damage over the course of the battle. Kaido’s scar will open on it’s own at a critical moment, which will give Luffy the opening he needs to defeat Kaido once and for all.
I think this would work for a few reasons. Firstly, Luffy wouldn’t specifically need to be stronger than Kaido for him to be defeated this way. He’d only need to be strong enough to push Kaido to the point that the scar opens on its own.
Furthermore, this would be a really poetic way for Kaido to go down. One of the main themes of Wano is loyalty, which is mainly explored through Oden and the Scabbards.
The Scabbards chose to use Oden’s attack out of loyalty to their lord, and if that very loyalty is what ultimately makes Kaido’s defeat possible, it would be a pretty conclusive payoff. Especially after Kinemon cried tears of shame, thinking that everything they’ve done was for nothing.
*Theory by Derpalooza