The movie takes place during the Pirates Expo, "made by pirates, for pirates", where pirates all over the world, including some of its most infamous ones, join in for a big treasure hunt to find a lost treasure, this time the treasure belonged to none other than Gold Roger!
Changing Tides: The Demon Heir's Freedom
After the Blackbeard Pirates broke into Inpel Down and made the Level 6 prisoners fight each other to the death, Jesus Burgess notices a single prisoner staring at them from a distance. He asks Marshall D. Teach about him, and Teach, shocked that the prisoner was still alive, informa Burgess that they were to leave him be. The prisoner, Douglass Bullet, is the "Demon Heir," a fearsome pirate who worked under the Pirate King Gol D. Roger. They leave Bullet to escape Impel Down on his own.
After some time passes, Bullet links up with Buena Festa, another pirate from Roger's who is also thought to be dead, and Buena devises a plan to gather famous pirates from around the world to resurrect the Pirates Expo. He explains to Bullet that they will put Roger's treasure on the line to create the dawn of a new era in piracy.
Suddenly, Law comes out of the Sunny's lower deck, looking noticeably injured. He reveals that this event is not what it seems and that Buena Festa is up to something. He was able to have his crew evacuate the island, but wants to investigate the matter further. Robin, Sanji, Chopper, and Brook go with him, and they depart on the Shark Submerge III; Robin manages to sprout wings to let it fall safely into the bay far below. Meanwhile, in Festa's underground lair, the Master of Festivities talks with Douglas Bullet, saying the time would be soon for them to put their plan into action.
The pirate crews make it up to the floating island, and they soon spot a wrecked ship surrounded by heaps of treasure. An all-out brawl quickly breaks out as the pirates fight to get to the treasure, and Luffy gets into fights with Scratchmen Apoo and Urouge while Zoro clashes with Killer. In the midst of the battling, Buggy manages to sneak toward the chest containing Roger's treasure and steal it. However, he is soon spotted and chased as the other pirates do whatever it takes to get the treasure.
On Delta Island, an undercover Smoker leaves an undercover Tashigi behind as he goes to investigate Buena Festa. Meanwhile, Law's group sneaks into Festa's lair, and Robin and Brook use their abilities to spy on Festa. There, they overhear Festa making plans with the World Government to have them set up a Buster Call on Delta Island, leaving them aghast. As they continue going through the lair, they run into Smoker, who immediately attempts to capture them. Sanji stops him from catching Robin, and she and Law run off while he battles Smoker.
Battle on Two Fronts: Douglas Bullet Arrives
Suddenly, an inconspicuous galleon travels up the Knock Up Stream and barrages the floating island with cannon fire, destroying it. The spectators, as well as Donald Moderate and Ann, flee in terror after this unexpected event, and all of the pirates fall down into the bay far below. While falling, Usopp finds himself next to the chest with Roger's treasure and grabs it. The pirates are left in chaos as the Devil Fruit users have to be saved from the bay by their comrades, and after the rescues are made, the pirates look in shock as they see Douglas Bullet holding a defeated Usopp. Luffy immediately confronts Bullet as the pirate attempts to kill Usopp, and Bullet ends up throwing Usopp at Luffy as he overwhelms Luffy with sudden speed. Bullet says that he wants to challenge the Worst Generation after hearing of their exploits, and he unleashes a massive blast of Haoshoku Haki that knocks out most of the pirates. Luffy, Eustass Kid, Killer, Basil Hawkins, Scratchmen Apoo, Capone Bege, Jewelry Bonney, X Drake, and Urouge stay behind to fight Bullet, while the remaining pirates move to flee from the island.
Bullet begins fighting the Worst Generation, and quickly overwhelms them with his sheer speed and immense strength. Apoo attacks Bullet with combat music, but the explosions do not affect him at all. Bullet easily bats away cannonballs shot by Bege and shrugs off X Drake in his allosaurus form. Bonney attempts to turn Bullet into a child, but he grabs her and slams her into the ground before she can get near him. Killer strikes Bullet with his swords, but Bullet easily blocks them with Busoshoku Haki, and he is not overwhelmed by Hawkins' Goma no So form. Bullet goes on to resist a strike from a powered-up Urouge, easily damage Bege in his Big Father form, and redirect two large attacks from Luffy and Kid to cause them to hit each other. Afterwards, the Supernovas are all left utterly overwhelmed, with Bullet not slowing down.
However, Luffy gets up and activates Gear Fourth: Snakeman. In this form, he barrages Bullet with rapid, direction-changing punches, though Bullet returns many of the punches. Their fight ends with each fighter giving the other a powerful punch to the face and sending them flying far away. However, as Luffy lays on the ground exhausted, Bullet gets up and is not any worse for wear. Bullet mocks the Supernovas' strength, saying they have not done nearly enough to reach his level. He then decides to step it up a notch and brings out his ship, the Catapult, from underground. He uses his Gasha Gasha no Mi abilities to change the composition of the ship and the iron weapons inside of it, forming them into a giant exoskeleton that he inhabits. While in the exoskeleton, Bullet states that the treasure of Roger that he currently possesses is the One Piece, shocking the Supernovas. In the exoskeleton, Bullet utterly overwhelms the Supernovas, who have no answer for stopping him. Bullet is able to make his already powerful exoskeleton even stronger by imbuing it with his Haki, and the battle ends as all of the Supernovas lie on the ground thoroughly defeated. Bullet prepares to kill Luffy by stomping on him, but Usopp tries to stop him by shooting projectiles at the exoskeleton. They appear to have no effect until one of them sprouts into a plant that tears off one of the exoskeleton's fingers, and Bullet responds by swiftly attacking Usopp.
Meanwhile, the rest of the pirates head to the coast, only to see the Buster Call fleet heading toward them. Sentomaru leads a battalion of Marines and Pacifista on the coast to attack the pirates, and the Foxy Pirates plead for the Straw Hats to protect them while the Buggy Pirates look toward Buggy. Admiral Fujitora makes his way to the coast, where he clashes with Zoro. The Bliking Pirates attempt to sail out, but their bow is suddenly sliced off by Dracule Mihawk on his Coffin Boat. His arrival is accompanied by the arrival of Boa Hancock and the Kuja Pirates, and the Marines uneasily think that the two Shichibukai have come to provide assistance, but are proven wrong as Hancock attacks them while looking for Luffy, and Perona attacks others with her Negative Hollows.
Underground, Sanji and Smoker continue fighting until Sanji asks about why the Marines agreed to work with Festa to send a Buster Call here. Smoker is surprised to hear the news, and receives a call from Tashigi revealing what is going on up above, causing him to abandon the fight to take care of business. Meanwhile, Law and Robin are approached by Crocodile, who has a plan regarding Bullet that he wants to share with Law. After speaking to Crocodile, they manage to find a map to guide them off of the island. Meanwhile, Buena Festa sits back on top of a tower as he contacts the Emperors of the Underworld to show what he has in motion. He reveals that Roger's treasure is an Eternal Pose pointing to Laugh Tale, and proclaims that with Bullet's possession of the treasure and quest to defeat every powerful person in the world, he will start a new era greater than the one Roger started.
The Marine battalion makes its way to the town, where they engage in a large-scale clash with the pirates. Koby, Hina, and Helmeppo participate in the fighting on the Marines' side, but the fighting is soon interrupted as Bullet makes his way to the town in his exoskeleton. Sensing the new development, Fujitora decides to depart from the coast, and brings down a meteorite as a parting gift. As the pirates around him wallow in terror, Zoro leaps toward the meteorite and manages to cut it in half. However, the two halves of the meteorite still threaten the pirates below, so Mihawk steps in and cuts it into tiny pieces before departing from the island.
Stopping the Stampede: A Teamup of Unprecedented Proportions
At the town, Bullet surveys the Buster Call fleet surrounding him and reveals that he awakened his Devil Fruit power. He then spreads out the composition of his exoskeleton and covers the entire town and Buster Call fleet with it, ripping it all apart and assimilating it into his creation, forming an enormous colossus the size of a mountain. The Marines and pirates are left in extreme panic, and the Marine Vice Admirals attempt to charge the colossus, but are knocked out in one punch, which is so powerful it tears apart the island itself. Bullet then raises the coast into high walls, preventing people from escaping the island. Festa proclaims that Bullet's treasure and power have ended the era, and the new era would be defined by the people's struggle to overthrow Bullet. He tells the Underworld Emperors that Bullet would kill all of them, and Bullet sets his sights on killing the Yonko. Meanwhile, Kizaru contacts Sakazuki about what happened, and Sakazuki orders for a second Buster Call to attack Bullet and Delta Island.
Meanwhile, at Marine Headquarters, Brannew briefs the Marines about Bullet's past. In his youth, Bullet was a soldier in the land of Galzburg, and ultimately massacred the people there. He proceeded to become a pirate and challenge Roger, who gave him a taste of defeat. Bullet joined forces with Roger and attempted to kill him many more times, but never succeeded in beating Roger before the Pirate King was executed. After Roger died, Bullet went berserk and headed on a rampage until he was finally stopped by a Buster Call led by Garp and Sengoku. In the present, Garp heads outside and talks with Sengoku, reflecting that Bullet lost his way after losing Roger. The two Marine heroes are very apprehensive about the threat the pirate currently possesses.
Meanwhile, a heavily injured Usopp carries an unconscious Luffy to find help. They stop in the path of a falling building, and Usopp stops a large pole from falling on Luffy, but collapses as the rest of the building starts to fall on them. However, Brook then arrives and stops the collapse by freezing the building, and Chopper arrives to treat their injuries. Usopp tells him to focus on treating Luffy, as he had lost a lot of blood. After receiving treatment, Luffy wakes up soon afterward. Usopp tearfully apologizes to him for not being strong enough to protect him, but Luffy has no issue with it and wants to go after Bullet right now. Despite Chopper's protests, Luffy activates Gear Fourth and flies toward Bullet.
The second Buster Call comes within view of Delta Island, and the Marines attempt to escape on a ship before the Buster Call starts attacking the island in mere minutes. Smoker elects to stay behind on the island, and Tashigi, Koby, and Helmeppo want to go with him, but Hina binds them with her Devil Fruit power and drags them away. Meanwhile, as Rob Lucci looks on at Bullet's colossus, Hancock searches for Luffy. She finds a red object surrounded in rock that she mistakes for Luffy's vest and pulls on it, only to realize that it is Buggy's nose. As Hancock and Buggy argue, Smoker comes up to them and attacks them, but is then stopped by Sabo, who fights him to a draw. Law then approaches the group as they see Luffy flying toward Bullet's colossus, which sees him and immediately overwhelms him. Luffy is sent toward Law's group's location, and Law tells the group about his plan to take down Bullet. He reveals that Bullet's creations could be weakened if they were broken apart, but Bullet's powerful Haki made them difficult to damage. Law says that he can cut a gap in Bullet's Haki with his abilities, but before he can go over the rest of the plan, Luffy flies off to attack Bullet again.
Bullet immediately overwhelms Luffy again and sends him flying across the island, and in retaliation, Hancock raced up the colossus and planted a powerful kick to its chest, sending it reeling back. The force of the attack enables Crocodile to come in and send a sandstorm toward the colossus, preventing it from fully reforming. Law then activates a ROOM and uses Shambles to replace parts of the colossus' right shoulder with other objects, leaving it weak enough to attack. Sabo and Smoker attack in unison, and succeed in blowing the colossus' right arm off. Bullet attempts to extend his shoulder to reattach the falling arm, but Buggy throws a Muggy Ball at it to prevent it from falling on him, completely destroying it.
Bullet is confident that he can overpower his enemies even with just one arm, and gears up to attack them. As he does this, Luffy inflates his fist to a massive degree and flies toward Bullet to attack him with it, resulting in their giant fists clashing. After a long and powerful clash, Luffy manages to overpower the colossus, and Law's group manages to debilitate it further with their combined attacks. Bullet is forced out of his colossus, but remains in his exoskeleton. However, the force of Luffy's punch causes the shots Usopp had fired earlier to sprout into plants, wrapping around and severely damaging the exoskeleton and injuring Bullet in the process.
As Bullet is forced out of his exoskeleton, both Crocodile and Rob Lucci attempt to take the Eternal Pose, but are stopped by Zoro and Sanji respectively. Bullet takes on Luffy in a brutal fistfight, and both fighters trade punches with impunity. Bullet uses his Haki to keep up with Luffy's ferocity, eventually covering his entire body in it. Luffy charges toward Bullet and inflates both of his fists, barraging him with Gomu Gomu no King Kong Gatling. This barrage eventually overwhelms Bullet and sends him crashing into the ground, defeated.
Following Bullet's defeat, Festa weeps and mourns over the failure of his plan. Sabo then comes to confront him, and Festa notes Luffy's ability to turn enemies into allies, saying he should have teamed up with him instead. Sabo replies that Luffy would never team up with someone like him, and Festa attempts to quickly shoot Sabo with a pistol, but Sabo strikes first as he uses Hiken to defeat Festa.
In the aftermath of the fight, Luffy stands with the Eternal Pose in his possession, and Crocodile and Lucci once again try to get it. However, Luffy decides to destroy it, saying he does not need it to reach Laugh Tale. He and his crewmates make it back to the Sunny, but their escape route is blocked by the Buster Call fleet. However, the other members of the Worst Generation start sailing out as well, posing a greater challenge to the Buster Call. Additionally, Smoker contacts Kizaru, saying to stop the Buster Call as there is no longer a need for it. Sabo returns to the Revolutionaries' ship, which has rescued Ann, and he asks Ann if she can form a certain illusion for him. As the pirates sail out, Kizaru attempts to attack them with many beams of light, but his attack is blocked by Sabo creating a wall of fire. The fire wall also gives the pirates a safe passage through the fleet, and as Luffy looks back, he sees Sabo along with an illusion of Ace made by Ann.
The Straw Hats are attacked by the bounty hunting Cidre Guild as their leader, Cidre, prepares to go to the Pirates Expo to kill Douglas Bullet. After escaping the Cidre Guild, Luffy disembarks on an island to replenish the Thousand Sunny's cola supply. There, he reunites with Hancock, and Cidre and the Cidre Guild attempt to kill the two of them. Luffy and Hancock manage to quickly defeat them, and Luffy obtains Cidre's Pirates Expo invitation, leading the Straw Hats to head to the event.