Chapter 859 is titled "Emperor Assassination Plan".
Cover Page Request: "Usopp throwing snakes onto Brook as part of a game of ring toss" - PN Orange Penguin, Tokyo
Inside the hideout of the Fire Tank Pirates, Capone Bege explains the details of his plan to assassinate Big Mom. As Luffy's group questions the possibility of physically injuring Big Mom, Bege explains his plan to trigger one of Big Mom's tantrums, as well as the plan to deploy the new gas weapons created by Caesar Clown. Bege also informs Luffy of his key role as the bait to distract Big Mom's subordinates, which Luffy readily accepts. Finally, all sides confirm that their alliance concludes upon their successful getaway, which will be via the Mirro-World, before wishing each other luck in executing their respective roles. Sanji then remarks that he must return to the Chateau to prepare for his "wedding", and all parties disperse to see to their respective preparations.
As the dawn of the wedding day breaks over Totto Land and the Germa Kingdom, their citizens awaken and begin to celebrate in anticipation. With the tea party's Underworld guests beginning to arrive, both Big Mom and the Vinsmoke Family are shown getting ready. At the same time, a fully-dressed Pudding muses to her homies that she hopes her dress will not become spattered with blood, before sighing about how tiresome it will be to have to modify the guests' memories at the conclusion of the ceremony.
Sanji, though not inherently interested in assassinating Big Mom, ponders how she can be killed, noting that she seems extremely tough. Pedro says they will need to do it quickly, with Nami recalling how the team was nearly killed retrieving Brook from her while she was sleeping. They then ask why they are aiming for her at the tea party, when several of her children will be around. Bege then replies that under certain conditions, they will have five seconds to take Big Mom's head. If they fail, then total war will erupt and their chances of success will be zero. Bege says the plan will start with Caesar Clown, and Caesar reminds Bege to refer to him by his alias, threatening to kill Pez if Bege does not uphold his end of the bargain and release him after the plan is executed. Caesar then presents the KX Launcher, which contains phosphorous poison that will kill anyone once it enters their body. However, not even that can pierce through Big Mom's skin, and so two conditions must be met: there must be no interference in the planned five seconds, and Big Mom's body must be weakened.
Pez starts to cry due to Bege's loud voice, and Bege quiets him down with baby talk. Bege tells the Sanji Retrieval Team about Big Mom's immense durability, with not even bullets or cannonballs being able to injure her. However, he did see Big Mom get injured once in the previous Tea Party. During tea parties, Big Mom puts a portrait of the mysterious Mother Carmel directly across the table from her. During the last tea party, a servant accidentally dropped the portrait, causing Big Mom to emit an earsplitting shriek that caused everyone to lose consciousness, as well as activate her Haoshoku Haki. When she kneeled down, her knee began bleeding. Thus, Bege plans to cut the picture in half, as not only will this leave Big Mom defenseless, but the people around her will be incapacitated from her shrieks for at least five seconds. Bege then presents the Sanji Retrieval Team with earplugs to protect them from Big Mom's shrieks. Luffy then suggests rescuing the Vinsmoke Family in the process, but Bege tells him that it will take three seconds for Big Mom to react to the portrait being destroyed, meaning there is a good chance they will die in those three seconds. Thus, Luffy will serve as bait to keep Big Mom's forces at bay. Nami and Chiffon are outraged that Bege is carelessly risking Luffy's life, but Luffy agrees to it, saying he has the perfect entrance planned. Luffy says the cue will be when Sanji and Pudding kiss, but Sanji reminds him that Pudding will shoot him before that, so he will dodge; Luffy will instead make his entrance once he hears the gunshot.
Bege says that once Big Mom starts shrieking, Luffy's group can rescue the Vinsmokes while Caesar will break in through a mirror with Brûlée's help. Once Caesar arrives, the team can escape the room and go back to their ships, where they can escape the island. The distressed Brûlée tries thinking of a way she can report this to Big Mom. After Big Mom's assassination is successful, the alliance will part ways, and Bege wishes everyone luck. With two and a half hours left until the wedding, Sanji prepares to go back to his room to prepare for the wedding, and Luffy asks Bege to help him with his entrance, to Bege's exasperation.
Meanwhile, the various islands in Totto Land celebrate the upcoming wedding, and in the Germa Kingdom, the soldiers of Germa 66 reflect on the peacefulness, having not been allowed at the wedding. In the Whole Cake Chateau, the Vinsmokes get changed for the ceremony. Meanwhile, Big Mom cries hysterically about Brook's death as she holds his lifeless skeletal substitute, but she is reminded about the wedding, and tosses "Brook" aside in glee as it is reported that her guests are streaming into the castle. In Pudding's room, Nitro and Rabian ask why Pudding is so sullen as she sits in her wedding dress. Pudding replies that she is not looking forward to being splattered in blood after shooting Sanji and having to rewrite everyone's memories in order to continue to be seen as a good girl.
- Bege explains his plan to assassinate Big Mom.
- Big Mom is revealed to have Haoshoku Haki.
- The alliance between the Straw Hat Crew, the Fire Tank Pirates, and Caesar will conclude once Big Mom is dead and all parties have made their escape.
- The day of the wedding arrives, with the Tea Party to commence in one hour.