WARNING: The following contains spoilers for One Piece, Episode 911, "Bringing Down the Emperor of the Sea! A Secret Raid Operation Begins!"
In the previous episode of One Piece, we learned about Kuri Town's past, where the daimyo of Kuri Town, Oden, brought order to the wild, untamed wastelands of the Land of Wano. That is, until Kaido and Orochi ganged up on Oden, bringing down the leader of this town and rebranding him as a traitor to the lands. However, his loyal samurai and sons -- the Akazaya Nine -- were sent 20 years into the future by Oden's wife -- who possesses the power of the Time-Time Fruit.
Now, in the wastelands of Wano, with the soils of Kuri Town intoxicated by poisons, it's up to the Straw Hat crew to overthrow Orochi and Kaido. But what does this plan entail?
THE MEN LOYAL TO THE OLD GUARD
When the samurai Kin'emon and his crew first arrived in the present-day Wano, after overcoming their existential fear of being in the future, he and his crew encountered the old retainers of Oden. They had waited for two decades for the "prophecy" of Toki, Oden's wife, to come true. In truth, Toki just told people that the samurai of Oden would return in 20 years, due to her using her Time-Time Fruit powers.
This led those loyal to Oden to conclude that they'd need to wait for the Akazaya Nine to return before they attacked Orochi and returned control over Wano to the rightful rulers. Those loyal to Oden have a Moon Tattoo on their bodies. However, the exact number of those loyal to the daimyo and his old guard remained unknown, which led Kin'emon and his samurai retainers to investigate.
O-Kiku infiltrated Kuri Town's culture, investigating both her allies and adversaries alike to gain intel. After all, the samurai had missed 20 years of history, which meant they had a lot to learn. In the meantime, Kin'emon, along with Kanjuro, Raizo, and Oden's son, Momonosuke, went out abroad to recruit allies.
The problem was, though, that on their way to reach Zou to find allies, they realized they were unable to sail, which pitted them against the likes of Doflamingo and, oddly enough, Trafalgar Law. Multiple enemies -- including Doflamingo -- are associated and affiliated with Kaido and his ilk. It was around this point, however, that Kin'emon first encountered Luffy and the crew, which led to the current events: the raid and liberation of Wano.
Regardless, Orochi believes the Akazaya Nine are dead, and that the prophecy foretells the coming of ghosts, not real men with real plots.
Kaido's forces are massive. Kin'emon, on the other hand, has managed to recruit Luffy's Straw Hat Pirates, Trafalgar's Heart Pirates, the Mink Tribe (Dogstorm's Musketeers and Cat Viper's Guardians), and samurai from within Wano still loyal to Oden. However, it would be unwise to start a war at this point, because the forces they'd attack would be insurmountable. Instead, it's wiser to sneak around and covertly defeat the very heads of Kaido's forces one by one. It is vital to prepare a plan to behead each and every leader.
Their mission will take them to Onigashima, where Kaido and his heads reside in their base. It would take a cross-sea journey to get there, but it's so close it's visible from the shore. In order to raid the ship, they will need a ship. They plan on attacking it on the Fire Festival -- a grand party for the whole land. That day, Orochi will go with his procession to the island. Once he arrives, there will be a banquet for the heads of Kaido's court, at which they'll get the men drunk and decapitate them all.
They will depart for Onigashima at 5:30 PM on the day of the festival -- a message sent throughout Wano to those with crescent moons on their ankles. The flyers contain a secret message that only those who know the secret will recognize. Naturally, members of Luffy's crew are already hard at work at this: Usopp is handing out secret plans; Franky is spying on enemy formations; Robin is spying on the elites, while the rest of the crew will continue to recruit people for the plan in ways that best benefit them. Carrot and Chopper will go to Cat Viper and his crew to help them with their tasks. All of them will work in secret disguises, like Usopp, Franky and Robin have.
Kin'emon won't see his wife, the tea shop owner O-Kiku worked for, until after the mission is over, who O-Kiku kept a watchful eye on. In fact, until the event happens, they need to stay split up. There's one final detail, though: Kin'emon wants Luffy to recruit three specific samurai before the raid who will be of vital importance in the final battle, and they have only two weeks to make the raid work.