Shiki (シキ) uses his Devil Fruit powers to destroy marine ships and warn Monkey D. Garp and Fleet Admiral Sengoku. On a floating island, Monkey D. Luffy is chased by a genetically-enhanced animal. The monster is overpowered by the other monsters before Luffy defeats the fourth monster. The Straw Hats have been separated into three groups: Sanji with Usopp, Roronoa Zoro with Tony Tony Chopper, and Nico Robin with Franky and Brook. Shiki tells Nami that she has been taken to the island against her will and a brief flashback is shown: several days earlier, the Straw Hats read news of an attack on East Blue. Luffy vows to protect the East Blue before witnessing Shiki’s ship overhead. After escaping a storm, Shiki meets Nami and reveals his powers to make any inanimate object he touches float. After learning it was Nami that delivered the warning, Shiki offers to take them there before abducting Nami. The others try to rescue her, but Shiki makes the pirates scatter on the island.
Shiki asks Nami to become his navigator but she refuses. His minion Doctor Indigo (Dr. インディゴ, Dokutā Indigo) demonstrates an evolved bird called Billy (ビリー, Birī), who can produce electricity, but Shiki rejects it after Dr. Indigo is electrocuted. He reveals that a plant, called IQ, can cause animals to evolve instantly and to increase strength along the way. Nami protects Billy, and the bird is left with her as Shiki and his men leave. Meanwhile, Sanji and Usopp battle various animals while Sanji searches for Robin and Nami. Meanwhile, Zoro and Chopper rescue a young girl, Xiao (シャオ, Shao), and are led to her village and are told about the large poisonous plants around the village. However, long term exposure to the plants is poisonous to humans, and the girl’s grandmother has become ill by it. Xiao was looking for the cure which is the IQ plant, but Shiki has stolen the IQ plants for his experiments. Sanji and Usopp learn that Shiki also takes all the men and young women to his royal palace, leaving the village with only the very young and old, before meeting up with Zoro and Chopper.
Nami flees with the help of Billy, and finds the Thousand Sunny along with Luffy. Robin’s group discovers that Shiki is planning to release the animals on the island into East Blue to force the World Government’s surrender and that he is planning a demonstration against a village on the floating island to show their power. The two join the others at the village, and they also learn of the plan from the village residents. Shiki confronts and defeats the Straw Hats and offers Nami to rejoin him on the condition that the Cocoyashi Village will be taken. Robin’s group arrives and rejoin the rest of the crew. Xiao gives them a tone dial and they replay Nami’s farewell message to Luffy, but he angrily leaves before the end.
Meanwhile, Nami attempts to destroy the plants protecting his palace, but gets poisoned herself. Shiki traps her near the plants and heads off to meet the pirate captains gathering. While greeting them, the Straw Hats launch a preemptive strike against Shiki and his henchmen. The group manages to defeat them while Chopper and Usopp are ordered to search for Nami. Nami is found by Billy who helps destroy the plants just as Usopp and Chopper arrive. Chopper soon realizes the only way to save Nami is to find the IQ medicine, but Shiki attempts to stop them. Luffy engages Shiki in a duel. The two find the IQ plant, but find the medicine is being held by Dr. Indigo. Zoro manages to defeat Dr. Indigo and Nami recovers. Sanji and Brook, meanwhile, witness another of Shiki’s henchmen, Captain Scarlet (スカーレット隊長, Sukāretto-Taichō), attempting to kiss Robin, but Sanji defeats Scarlet.
Nami, Usopp and Chopper trick Shiki into redirecting his ship to the island, forcing his crew to flee. The Straw Hats rig the palace with explosives. Shiki refocuses his attention on the Straw Hats, but Luffy uses an electric charge and knocks Shiki to the ground, leaving Luffy victorious. The other Straw Hats escape with the Thousand Sunny, using Shiki’s pirate sail as a parachute. Luffy is recovered by Billy while the villagers are shown flying away using the wings on their arms. The Marines capture the retreating pirates, including Shiki. As the Marines witness the islands crash into the sea, now free of Shiki’s power, they spot the Thousand Sunny. However, the Straw Hats escape. Luffy later learns that Nami’s message was actually a coded SOS directed at him that the crew took as a love confession; he tries to listen to the end, but Nami throws it overboard in embarrassment.