Luffy’s Gear 4 has been shown to be completely useless against both Big Mom and Kaido, and Luffy still doesn’t seem like he’s fully mastered the stamina of it, so Gear 5 is out of the question.
A lot of people have been saying Kaido will be taken down as a group, but I think there’s a way to give Luffy a 1v1 fight alongside a power-up and have his allies be involved.
Gekko Moriah was teased as being active in the New World alongside Abasalom right before Dresrossa. Moriah had a tragic backstory where Kaido killed his entire crew and he felt the need to create a zombie crew so he wouldn’t have to face the fear of witnessing his crew dying in front of him again.
Moriah probably loathes Kaido more than any character we’ve seen so far, so if Oda wants to introduce him into the New World, this arc would make the most sense to do so. I’m under the impression that Jinbe’s speech about how lazy he had gotten during Marineford prompted him to get back into shape and I think his post-timeskip appearance will resemble how he used to look when he was younger like in the chapter 0 Strong World prequel.
While Moriah obviously hasn’t been friendly towards Luffy in the past, Luffy teamed up with former enemies several times throughout the series, and considering that Kaido was the one who ruined Moriah’s entire life, I’d wager his hatred for Kaido outweighs his hatred for Luffy and he’d take delight in the opportunity to take Kaido down. Nightmare Luffy was the reason Luffy was able to defeat Oars in Thriller Bark, and Luffy was unstoppable being filled with just the strength of the shadows of random pirates and marines who were captured on the island.
If Moriah assists Luffy in defeating Kaido, imagine a Nightmare Luffy “2.0” that would not only potentially combine with Gear 4, but Luffy’s allies such as Law, Kin’emon, and Marco alongside the entire Straw Hat crew offering their shadows to assist Luffy and power him up. Not only would Luffy gain the strength of all of those powerful characters, but imagine Luffy being able to use swordsman skills from Zoro, Kin’emon, and Brook on Kaido. He’s been carrying around one of the legendary swords so far this arc and this would give him a reason to use it.
What do you guys think of this idea? It would put Luffy on Kaido’s level without feeling like a power-up from out of nowhere and Luffy would simply be borrowing the extra strength from his allies.
*Theory by MeanMustacheMan
