WARNING: The following contains spoilers for One Piece Episode 909, "Mysterious Grave Markers! A Reunion at the Ruins of Oden Castle!"
Luffy and the gang have pushed forward with their war against Kaido's machine of domination on One Piece. After returning a massive carriage of food to the innocent villagers, Luffy looked ready to restore order to the Land of Wano, where the poor can live with fresh food and water, and won't fear being poisoned in their beds..
But Luffy has started something: a civil war against the powers that rule Wano. And Trafalgar D Water Law intends on showing Luffy something important before they set off on their next adventure. He guides Luffy, Zoro and Ochiku up the mountain to the ruins of Oden Castle, which might reveal the secret history of Wano.
The Ghosts of Wano
Trafalgar takes the crew to a set of enigmatic grave markers at the ruins of Oden Castle. However, as they continue there, they're charged by monster armed with a sword in his mouth. Zoro stays behind to hold off the beast -- a gigantic, scarred tiger -- sensing its thirst for blood.
Meanwhile, at the Flower Capital, children are indoctrinated with a false lesson of history: Kozuki Oden and the Akazaya Nine did something sinful. It's a name children are taught is wrong to even repeat. By contrast, they're told the Shogun Orochi was a hero who defated the evil samurai 20 years earlier. It's a story many of the old folk recognize as false, designed to keep the children from questioning the tyrannical order of things.
The only people who can criticize Orochi are drunkards, like the money lender Kyoshiro, who, it just so happens, is being fed alcohol by Nico Robin in disguise. Nico learns of a curse left by Oden -- that the spirits of the nine fallen samurai would return on the 20th anniversary to cut down Orochi. Apparently Orochi fears the ghosts will come to exact their revenge, despite many of his underlings wanting to fight the ghosts for glory -- if they even believe they exist.
The Ruins
Luffy is surprised to find the castle is completely burned. They find the markers for Oden and the Akazaya, only to discover names that Luffy recognizes, like Kin'emon. On the way to Wano, Luffy couldn't get in contact with Kin'emon, which now forces him to confront a possible reality: Did he and the others die?
However, it turns out that Kin'emon and his crew had always been dead. To Luffy's bewilderment, all of the people he traveled to Wano to meet had been dead this entire time -- or, at least presumed dead. They had actually faked their deaths years earlier.
Ochiku greets Kin'emon with an intense hug, visibly shocked that they're OK. She learns they're the heroes brought to fight and overthrow Orochi as part of the planned revenge against those who overthrew Oden Castle. At that moment, the rest of the Straw Hats happen to arrive, charging in with smiles. In one fell swoop, the Straw Hats are reunited -- save for Brook, Nico and Usopp. The rest of Trafalgar's crew, except for Bepo, who has diarrhea, unite as well, turning the castle's ruins into their headquarters for their coordinated rebellion.
It is here where they are told by Kin'emon one more secret they must know before proceeding -- one they won't believe if they hear it. All of the Akazaya -- including Ochiku -- time-traveled 20 years from the past.