The movie opens with the Straw Hats receiving a mysterious invitation to a luxurious recreational island, promising them the time of their lives. Upon arrival, they are greeted by the eccentric and flamboyant Baron Omatsuri, who claims to be a former pirate captain. The Straw Hats are initially skeptical but soon find themselves enjoying the island's various amusement park rides, games, and activities.
However, things take a dark turn when the Baron's henchmen, led by a mysterious figure known only as "The Strongest Under the Heavens," begin to sow seeds of distrust and division among the Straw Hats. They pit the crew members against each other, causing arguments and disagreements that threaten their unity.
As the Straw Hats' situation becomes more dire, they begin to uncover the dark secrets of the island and the Baron's past. It is revealed that the Baron's former crewmates were all killed in a treacherous betrayal, leaving him as the sole survivor. Tainted by his trauma and desire for revenge, the Baron has become obsessed with separating and destroying close-knit groups of pirates.
One by one, the Straw Hats are captured and forced to participate in deadly games and challenges, pushing their physical and mental limits to the brink. Luffy, desperate to save his friends and uncover the truth about the island, faces off against the Baron in a final showdown that reveals the sinister nature of the island and the true identity of "The Strongest Under the Heavens."
In the end, Luffy and his crew triumph over the Baron and his henchmen, reconciling their differences and reaffirming their bonds of friendship and camaraderie. The movie ends with the Straw Hats sailing off into the sunset, ready for their next adventure.