Back in chapter 920, Kin’emon explaines that they don’t plan on waging a war, but rather strike when their enemy is off their guard.
And in chapter 951, we see that Ashura sure has been working hard. He managed to gather a ton of ships, enough to carry thousands of soldiers. Kin’emon then says that he will let Franky “repair” them. But we know Franky better than that, he wont just repair them, of course! So what will he do exactly? This brings me to my next point!
Their plan is solid, to invade Onigashima when everyone is too busy partying, and will probably be drunk. The timing sure is solid! However, you have to assume that even during the fire festival, there would still be stationed guards on the lookout for enemies, and a huge fleet slowly approaching sure isn’t hard to miss. The guards will alert Kaido, who would take five minutes out of his celebrating to completely obliterate the armada. They’d be literally dead in the water, without even reaching the shore. So how will they manage to actually get everyone to Onigashima, when there’s an enormous dragon that can destroy you from a km distance?
Well, I think the answer was given to us this very chapter as well!
Yes, within this little panel that Oda just snuck in, the answer lies! Oda wouldn’t mention this if it had no meaning whatsoever. My prediction is that Franosuke will make the armada into skyships! Thousands of these skyships will be released on the day of the fire festival, as they always do, meaning no one will raise an eyebrow if they were to drift over Onigashima. And spotting a difference in sizes between the ships would be difficult when they’re a couple of hundres of metres in the air!
*Theory by milky-cow
