As the climax of the Yonko saga, the battle of onigashima has been filled with unforgettable moments and imaginative surprises. After the excitement of roofpiece, I foresee Oda giving fans a second round of group battles to close out what has been the most ambitious saga of one piece. Based on the fact that we aren't anywhere close the end of one piece (~5 years is still a long time and I am confident that Oda gave us a gross underestimate) and the unformulaic narrative style of the battle of onigashima, I theorize that the war will be determined by two grand finale battles, Big Mom vs. Law/Kid/Sanji and Kaido vs. Luffy/Zoro. Below I present arguments supporting my theory:
1) The simultaneous Zoro/Sanji pair battles: The raid has not been following the traditional one piece end of arc combat formula whereby the straw hats' respective battles are played out, more or less, in order from weakest to strongest member. Instead, we had Zoro pair up with Luffy in roofpiece, the high tier Jinbei fight early on, many significant non-strawhat battles and Ussop/Chopper not having classical combats (for the time being...). So instead of this stairway structure from least to most important fight, Oda has been consistently flip-floping between two or more battles at any given time. I think he's doing this to artificially make battles seem longer although they in fact take up less pages than normal, and also because it keeps the reader excited and updated as to what is going on. After 1033, there are really 3 pairs of narratives going on; the 2 Yonko battles, the 2 All-Star battles and the CP0 situation + Yamato situation (there are also a few more threads that aren't really the focus now). The way that Zoro and Sanji battles are playing out indicates that they are very likely to finish at the same time, at which point two top tier fighters will be left with nothing else to do unless they are both severely injured beyond short-term recovery. So what would Zoro or Sanji do once they complete their battles while the war rages on?
2) The King and Queen contradiction: Around the point where most of the "fodder/weakling" battles were finishing up (I don't exactly remember when but I think after the tobiropo were taken out), it was made clear that the All-Stars could easily sway the tide of the onigashima battle regardless of the current losses on the side of the Beast pirates. I believe this implies that if left alone, the All-Stars could sway the outcome of the Yonko level battles and shift the battle in their favor which makes sense as everyone can agree that YC1 and YC2 aren't no-diffs to Yonko level fighters (I would estimate high-diff and mid-diff for YC1 and YC2 vs. Yonko respectively in a serious fight). So in a world where plot armor didn't exist and King and Queen won their fights, it's not hard to imagine that they would go and participate in Yonko fights even if only so as to provide basic support. Furthermore, we already see that YC1/YC2 fighters have so far participated in multiple battles on onigashima; For Zoro roofpiece and King, for Sanji BlackMaria and Queen, for King/Queen Marco then Zoro/Sanji.
3) The Big Mom and Sanji resolution: Wano arc and the raid on onigashima have been filled with coincidental moments of characters barely missing each other. For example Momo and Hiyori intentionally not meeting before the raid, and Yamato barely missing Sanji and Brook/Robin in recent chapters (off topic, but my bet is she will run into Zoro very soon). One reunion that I am very eager to see happen and I feel has slipped under the radar is Big Mom and Sanji. I personally feel that Sanji fighting Big Mom could draw out his current personal transformation and past family trauma to its conclusion. Especially note that fighting Big Mom would require that he intentionally fight a woman. Therefore, I really feel that Sanji's participation could bring the emotional impact that the Big Mom fight has been lacking so far (note how neither Kid or Law have had any business with Big Mom until onigashima roofpiece).
4) The final Yonko turn tables: Last time we saw Kid and Law facing Big Mom, they revealed their awakening abilities which were off-screen powerups to deal a massive blow to Big Mom. However, she gets up right after and showcases her own mega-evolution powerup making Kid/Law outlook to win solo seem unlikely. They just showcased the peak of their devil fruit abilities and now have practically no new strategies to take on this new Big Mom form (and no! Kid will not get CoC coating. I don't think Oda will make the amateur move of giving 3 characters the same powerup in the same arc. Talk about supersaiyan bargain sales). Therefore, I feel the current situation would benefit from Sanji's participation once he's done with Queen. I also believe the current Big Mom situation will be mirrored with Kaido vs. Luffy whereby Luffy will showcase the new attack(s) Kaido mentioned after he knocked Luffy off of Onigashima and then be one upped by an unforseen Kaido powerup, making Kaido seem insurmountable at Luffy's current power level and thus requiring Zoro's aid.
5) The Luffy powerscaling problem: Kaido is the strongest creature in the world (one of only a handful of strongest ... titles) and is arguably the current strongest fighter alive in one piece (please note the "arguably"). Given that one piece will probably have one more entire saga (series of linked arcs) left in the series, having Luffy beat Kaido one on one would create a lot of problems for his character and the story because Luffy would simply have become overpowered too early. Now I don't want to dive too deep into another series, but this is exactly the problem Naruto ran into from the Pain arc onwards because the protagonist just became so ridiculously overpowered relative to the supporting cast that every conflict in the Great Ninja War was a simply a question of "Where is Naruto?" and "Is Naruto here yet?". Remember that Kaido really is on the same level as Shanks, Blackbeard, Marine Admirals etc. in our minds, so unless you want the climax of one piece to be Luffy talk no jutsuing blackbeard, then don't expect Luffy to beat Kaido single-handedly. Now one might argue that Kaido having gone through marathoning battles since the start of the raid and Yamato's comment that his power is weakening might nerf him enough to allow for Luffy to 1v1 Kaido, but I simply don't think that's enough to merit the formulaic shonen battle struggles that Luffy should face when fighting against the major one piece fighters of the next and final saga. I know that Luffy did proclaim that he would win alone against Kaido, but I think that Oda is trying to set up Luffy's next personal goal for the rest of the series. As the motive to get stronger for his nakama became the cornerstone of Luffy's character after marineford, Luffy being unable to beat Kaido 1v1 will help him set a new personal beacon for the rest of the series and reaffirm his commitment to becoming stronger to protect his freedom and that of the friends/territories/allies he has made along his journey. In my mind, Oda has already accomplished his goal for the arc which was to confirm that Luffy is at the level of the Yonkos but just not at the top of that short list YET. That is why having Zoro join Luffy in the final battle against Kaido will help keep Luffy's powerscaling in check and allow us the catharsis of having Kaido acknowledge Zoro properly as an Oden level samurai (and ZKK too ;D see point 7).
6) The Zoro/Sanji powerscaling problem: Due to Zoro and Sanji's lack of truly meaningful and transformative battles through the Yonko saga, they currently face the opposite powerscaling problem that Luffy has. Before wano, these 2 were too weak for the top tier battle feats we should expect from them in the final saga of one piece. Zoro and Sanji might have to face admirals, top-level revolutionaries and/or other pirate captains (I don't know of course but the idea is that they will likely face top level characters of the one piece world). So although one might argue that having Zoro/Sanji beat a YC1 and then also have a hand in beating a Yonko would be an insane amount of accomplishments in one arc, I would say that Oda is accelerating their growth because they didn't get 2-3 arcs of significant growth as Luffy has through his fights with Doflamingo, Katakuri and Kaido (prior losses). It seems that the last arcs have focused narratively on Zoro and Sanji so that they can come to the right level of maturity whereby Oda can choose to focus more on the other strawhats (Nami and Ussop at least) in the final arcs before the conclusion of one piece.
7) ZKK (rational zoro fan here :D): Instead of going through the massive dump of ZKK evidence that most of you have probably come across, I only wanted to address 2 common ZKK counterarguments I have been hearing a lot since roofpiece. Many youtubers have been saying that ZKK won't happen because it undermines Luffy or that Zoro would only execute Kaido after Luffy defeats him. With regards to the undermining Luffy argument, my previous points show that I personally believe this arc isn't "mainly" about Luffy. Yes, if the arc ends with group battles he will not have defeated Kaido, but instead he will have solidified his position as the 5th Yonko, reiginited his passion for getting stronger, and proven his leadership abilities by being the face behind the take down of two Yonkos. So I think wano will have a lot of awards and accolades moments of greatness for Luffy in the post onigashima period (perhaps a 1-2 reverie-size mini arcs where different parts of the world are being hit with the news etc.), but the key battle accomplishments will fall to Zoro and Sanji to prove they are ready to act as the "wings of the pirate king". Regarding the second argument that ZKK would only happen after Luffy solo beats Kaido, such a scenario would just be insulting to Zoro fans and mischaracterize the relationship between the captain and his firstmate. Having the duo fight and take down Kaido together would be reminiscent of their first battle together against captain morgan, and is also hinted at by Zoro's last line in 1033, which to me expresses his desire to quickly powerup to his captain's level so that he can fight besides him in his most desparate and challenging moment!
I hope you enjoyed my theory analysis. Please make sure to share your thoughts and participate in the poll at least!
