Chapter 854 is titled "What Are You Doing?".
Nami and Jinbe run through the Whole Cake Chateau and battle Big Mom's forces before being pulled into the Mirro-World by Chopper and Carrot. Inside the throne room, Pudding and Big Mom go over the plan to assassinate the Vinsmoke Family while Big Mom is still holding Brook. Meanwhile, the Big Mom Pirates have a meeting to ensure that the Sanji Retrieval Team is indisposed and the Vinsmokes are in their proper place. However, Opera lies that Luffy and Nami had burned to death in order to prevent him from losing face and being punished, and a guard mistakes a servant sleeping in Sanji's bed for the actual Sanji. Bobbin discovers Sanji in the hallway soon afterwards, and tries eating the meat that is meant for Luffy, which causes Sanji to kick him into the wall. Knowing now what he has to do, Sanji runs off.
Big Mom's forces chase after Jinbe and Nami, intent on surrounding and trapping them. They then recognize Jinbe with a shock and realize that he is rebelling, and Jinbe asks Nami to take care of the soldiers chasing them from behind. As Jinbe races toward the forces heading to them from the front, Nami uses Thundercloud Rod to shock the ones behind them. However, she accidentally shocks Chopper, who had emerged from a nearby mirror in order to rescue them. Nami and Jinbe entered the Mirro-World, where they reunite with Chopper, Carrot, and Pedro. Brûlée sees Jinbe and realizes he has rebelled against them, having heard earlier that he had backed out of facing Big Mom's roulette while trying to quit the crew. Jinbe affirms this, saying that the wheel would have brought nothing more than death and ill will, and Pedro states that he made the right choice, as his comrade spun the wheel five years ago and had his entire lifespan removed. Brûlée laughed and stated that that was the point, as Big Mom does not let people leave Totto Land alive. However, she is interrupted as the Sanji Retrieval Team boards the carriage to look for Luffy, Brook, and Sanji, though Diesel is barely able to pull such a heavy load.
In the Queen's Chambers, Prometheus puts a bandage on a wound that it received from Brook after the wound became deeper, upset by the pain. Big Mom commends Brook for managing to give her top homies their first injuries, and Pudding asks if she is going to continue carrying Brook around. Brook is surprised by Pudding's bluntness, and Big Mom states that since she is mesmerized with Brook she will carry him around instead of putting him in the museum for the time being, and Brook is appalled by his new fate. Big Mom then commends the rest of the Straw Hats for making it through the Seducing Woods and ending up in the Prisoner Library, and Pudding asks if Big Mom is going to kill them after the ceremony, which she affirms, shocking Brook. Big Mom states that the Vinsmoke Family is likely intoxicated after she sent barmaids to them, and Pudding reveals that Reiju went sneaking around, but she dealt with her. Big Mom shows concern about the encounter, warning her daughter that an encounter that goes wrong could jeopardize the wedding, but Pudding reveals that she did get to test her gun out on the Vinsmokes' bodies, which blows through them. Big Mom laughs and gleefully plans out the wedding assassination. When Sanji lifts Pudding's veil, he will see her third eye and falter, allowing her to shoot him through the head, giving the Big Mom Pirates the signal to commence the attack. Before the Vinsmokes will be able to react, they will face countless numbers of guns pointed at them, and their blood will stain the floors as gunshots ring out all over the room. The Big Mom Pirates will then begin the real celebration, eating cake and black tea as they gain control over Germa 66.
Meanwhile, a Chess Soldier peeks into Sanji's room, reports that Sanji is indeed sleeping in there, and receives orders to not let anyone in or out of there. However, the servant who attended to Sanji is actually the one in the bed, and he wakes up in shock that he fell asleep in Sanji's bed. However, since Sanji is not back yet, the guard decides to get a bit more sleep. In the meeting room on the second floor, Mont-d'Or goes over the Sanji Retrieval Team's statuses, knowing that Pekoms was with them until they entered Totto Land and that Pudding led six people to Whole Cake Island. Brook is currently in Big Mom's hands, and Mont-d'Or confirms with Count Niwatori, who survived Pedro's explosion, that Pedro blew himself up. They had received a report from Brûlée that she had captured Chopper and Carrot, and now the only outstanding problems are Luffy and Nami. The two of them were supposedly imprisoned, but Mont-d'Or had heard rumors that they had escaped, and confronts Opera as to why this and rumors about Jinbe's appearance have circulated around. Opera vehemently denies the rumors, saying he never saw Jinbe and that he burned Luffy and Nami to death due to them not having any information on Lola. As he says this, Opera notes in his mind that there is no way he could say the rumors are true, as Big Mom would definitely punish him by removing his lifespan. Mont-d'Or reluctantly decides to cross out Luffy and Nami as well, and asks about the whereabouts of the Vinsmoke Family, to which he receives confirmation that they are in their rooms. Mont-d'Or then adjourns the meeting, happily stating that the intruders are gone and their goal now is to prepare for the wedding to make it as good as possible. However, he tells the Chess Soldiers afterwards to continue keeping watch, as he does not trust Opera.
In the third floor infirmary, Reiju looks out of a window at Sweet City, where a weak Luffy is stumbling to the spot where he agreed to meet Sanji. Inside the Chateau, Sanji sits on a bench as he considers the basket of bento he prepared for Pudding, reflecting that it was surprising he made this for Pudding since it contained all his crewmates' favorite foods. Sanji accepts his oncoming death at the wedding tomorrow, thinking that it was for the best since Germa would be exterminated and Big Mom would be happy, giving his crewmates their best chance to escape. Bobbin then approaches Sanji, surprised that the latter is not in his room as he takes out a piece of meat from Sanji's basket. However, Sanji remembers Luffy's declaration that he would not eat anything until Sanji fed him again, and he kicks Bobbin over the head, saying the meat was not for him. Bobbin slams into the wall, and Sanji reclaims the meat he made as some of the guards race toward the disturbance. A bewildered Bobbin asks what Sanji is doing, causing a shocked Sanji to give himself a mental shake before running off with the bento basket in hand.
- Chopper pulls Jinbe and Nami into the Mirro-World.
- It is confirmed that Jinbe never spun the punishment roulette wheel as he knew that it was rigged to maim or kill the spinner every time.
- It is revealed that Brook is the first being to ever injure Prometheus.
- Despite being a "sun" homie, Prometheus is revealed to have arm-like appendages.
- Big Mom's plan to assassinate the Vinsmoke Family is explained in more detail.
- Brook learns of both the plan and Pudding's true nature.
- The Charlotte Family and the Big Mom Pirates hold a meeting.
- Tamago is revealed to have survived Pedro's dynamite explosion.
- They are unaware of Brûlée’s defeat by Chopper and Carrot, and they believe that Pedro, Luffy, and Nami have died, crossing off all five of them as threats for the wedding plans.
- Sanji injures Bobbin before running off.