Chapter 731 is titled "Operation Dressrosa SOP".
Caribou's Kehihihihi in the New World Final - "Thank You Pirate Caribou, Who is as Sweet as My Grandson".
At the flower field, Thunder Soldier explains the layout of the secret underground factories and trade port as well as the toy slaves and the dwarves held underground. He also reveals the identity of the Devil Fruit user responsible for turning people into toys and the frightening nature of her powers. He believes that the defeat of the girl Sugar would undo everything caused by her.
In the Colosseum, Luffy manages to find Bartolomeo and Bellamy during his search for an exit. Luffy is reluctant to leave the Mera Mera no Mi, but he has no choice since his crew are in danger. Fortunately, Bartolomeo agrees to win the Devil Fruit for Luffy. However, a stranger appears and tells Luffy that he cannot have it, earning him the irk of Bartolomeo but the stranger easily brushes him aside as he approaches Luffy who looks at him in tears.
At the center of the Colosseum, Acilia has teamed up with Rebecca to ensure her chance to reach the finals. Meanwhile, outside the Colosseum, Luffy manages to escape with Zoro and Kin'emon as the trio disguise themselves as fish toys. Zoro questions Luffy about why is he still crying, but Luffy says that everything is fine.
Elsewhere, in the middle of an alley, Koala is communicating with the stranger who met Luffy, who is donning Luffy's Colosseum disguise and told him that he must get Ace's Devil Fruit back. Luffy is still reeling from the fact that the stranger he met was someone he thought was dead a long time ago.
Bellamy is seen panting and hurt badly on the ground, with Bartolomeo having formed a barrier to protect him from Dellinger. Dellinger injures his leg trying to break through the barrier and shouts to Bartolomeo to get out of the way and let him finish his mission, but Bartolomeo refuses. Having been given a new mission by Diamante to go and guard the SMILE factory, Dellinger decides to leave Bellamy be but promises to deal with both of them later. Bellamy wonders why a stranger like Bartolomeo was helping him, to which Bartolomeo replies that once he fights along with someone, he considers him a friend.
Back at the Flower Hill, Thunder Soldier is briefing everyone about his plan, called Dressrosa Operation SOP. He goes on to explain the existence of a secret underground world operating in Dressrosa, which involves illegal transactions. The factory, which is also tied to the underworld, function with the labor of the captured Tontatta citizens and the people turned to toys. The resistance has been building a secret tunnel, which they will now use to enter the area and destroy the factory. Before that, however, they must succeed in defeating an agent of Doflamingo, in order to make her power lose effect thus returning the toys into their human selves and restoring the citizens' memories. Hopefully, by achieving that, more people would join their cause. When asked by Usopp where that Devil Fruit user is, Thunder Soldier answers she must be at the underground port and, due to her Devil fruit's side effect, which has kept her from aging, she is guarded by Trébol himself. Usopp rejoices, when he hears he is up against a little girl and a pumped up Franky asks the Dwarves to take them to the underground tunnel.
Back at the Colosseum, Luffy, who was looking for an exit, bumps into Bartolomeo and Bellamy. Bartolomeo, excited to meet his idol again, asks him reluctantly if he met with Zoro. When Luffy states his desire to find an exit, Bellamy tells him that such a thing does not exist in the Colosseum, because it was built in a way to prevent the contestants from escaping once they enter. Luffy, surprised, asks Bellamy to show him the exit, since he must know where it is, being Doflamingo's underling. Bellamy shouts he would never betray his captain, but says that he will be heading for the exit himself, so if Luffy was to follow him he could find the exit, too. Bartolomeo wonders why Luffy would give up the fight for the Mera Mera no Mi, to which Luffy replies that his friends' lives are more important. Bartolomeo promises to get the fruit and give it to Luffy, which was his original plan anyway.
At that point, a man walks in stating that the fire fruit cannot go to Straw Hat Luffy. Bartolomeo confronts him for speaking to his idol like that, but the man simply pushes him away. Upon looking at the mysterious man, Luffy is greatly shocked and starts shedding tears of joy.
When Luffy finaly finds his way out, he meets with Zoro and Kin'emon again, with the latter providing animal outfits for the three of them, in order to escape the Marines and leave the area unnoticed. Zoro is irritated by Luffy's non-stop crying and tells him to cut it out. Luffy, still sobbing and shocked, wonders how is it possible for "that man" to be still alive.
A young woman is seen sitting on top of a bunch of defeated men, speaking through a Den Den Mushi, stating that Robin is in this country and that she desires to see her again. The woman is none other than Koala, who has become a member of the Revolutionary Army and is a Fishman Karate substitute instructor. She goes on to ask the receiver of the call, if he met the man he was looking for and if he had any news on the situation underground. Then the man is shown, who is the same man seen talking to Luffy earlier, wearing "Lucy"'s attire, stating that he has to go get Ace's fruit back and inherit his will.
A flashback of Ace's grave is then shown, with three cups in front of it, confirming that the mysterious man was none other than Sabo, who was presumed to be long dead by his brothers.
- The old woman knew Caribou was not her grandson.
- This chapter marks the end of Caribou's cover story.
- Bellamy is saved by Bartolomeo, and Dellinger is called away by Diamante to guard the SMILE factory.
- Thunder Soldier named the decisive operation to overthrow Doflamingo "Dressrosa: S.O.P."
- Sugar, the little girl in the Donquixote Pirates, is revealed to be the toy maker and user of the Hobi Hobi no Mi. It is said that her body stopped growing after she consumed her fruit.
- Trébol is Sugar's bodyguard.
- Luffy, Bartolomeo, and Bellamy encounter a stranger, who is revealed to be Sabo who is currently a member of the Revolutionary Army.
- Bartolomeo reveals he entered the fights so he could win the Mera Mera no Mi and personally return it to Luffy.
- Rebecca and Acilia have teamed up in the Corrida Colosseum.
- Koala returns and is part of the Revolutionary Army.
- She seems to know Nico Robin.
- She is also a Fishman Karate substitute teacher.
- Sabo takes Luffy's place as Lucy in the Colosseum.
- Luffy escapes the Colosseum, making his way to the palace with Zoro and Kin'emon, while disguised as animals.
1: new introduction
2: new member