It was a time when pirates ruled the seas. Several bands of pirates were battling over the great hidden treasure, One Piece, which was left by the now legendary pirate captain, Gold Roger. There was a young boy who admired the pirates, his name was Monkey D. Luffy. One day, he mistakenly eats the devil's fruit and turns himself into a rubber human being. Ten years have passed since that incident. Luffy sets out to sail all alone. He sets out to become a great pirate captain and that's when his great adventure begins. "I'm going to be the Pirate King! I'm going to get One Piece!".
With Nami forming an alliance with the crew as their navigator (though not as an actual member), the crew arrives at the Syrup Village, where they meet the town liar, Usopp, who too has ties to Shanks.
When trying to convince his rich friend, Kaya, to give the Straw Hats a ship, Usopp is told to stay away from her by her caretaker, Klahadore. However, when Usopp and Luffy later see him conversing with a strange man, they learn of a plot to kill Kaya.
After learning of Captain Kuro's evil plan, Usopp runs back to the village to warn Kaya, only to find that after all his years of lying no one believes him.
Usopp resolves to keep his story of pirates attacking the town a lie by making sure none reach it. Luffy, Zoro, Nami, and Usopp then try to keep the Black Cat Pirate Crew at bay.
The Straw Hats manage to take out most of the opposing Black Cat Pirates, so Jango orders the Nyaban Brothers to attack. Meanwhile, after getting hypnotized by Jango, Luffy gets himself stuck under the collapsed mast of the Black Cat Pirates' ship.
Captain Kuro himself arrives at the scene, and with Zoro too injured to fight, Luffy being incapacitated, and the other two being too weak to handle him, things seem hopeless. However, Kaya herself appears to bargain with Kuro.
Zoro and Buchi (of the Nyaban Brothers) face off once again as Luffy and Kuro begin their fight. Usopp orders the Usopp Pirates to run away with Kaya, but Jango goes after them. A flashback reveals how Captain Kuro faked his death with Captain Morgan and how he became Kaya's butler.
As the fight between Luffy and Kuro is close to an end, the Usopp Pirates do their best to avoid Jango.
Kuro's ultimate attack, "Shakushi", attacks everything in the area, whether friend or foe, and Luffy becomes enraged by his lack of regard for his crew. Will Luffy's determination overcome Kuro's sheer speed?
With Usopp now in the crew and a new ship, the Going Merry, under their command, the Straw Hats head to an island said to hold a fabled treasure, only to encounter a strange man stuck in a treasure box that has also been looking for this treasure.
While Usopp & Luffy fool around with the ship's cannon one day, Zoro dreams about his childhood and the promise he made to Kuina.
The crew meets Johnny and Yosaku, Zoro's former companions, and they set sail for the Baratie restaurant in search of a cook.
Sanji, a cook at the Baratie, helps a starving pirate named Gin. Luffy begins his job as a waiter to pay for the damage he did to the Baratie, and tries to convince Sanji to join his crew.
Gin returns to the Baratie with his also-starving captain, Don Krieg, to whom Sanji once more gives food, but Don Krieg betrays the cook once he regains his energy.
It is revealed that Chef Zeff was a great pirate known as Red Leg Zeff. Gin explains the catastrophe the fleet met in Grand Line when they encountered Hawk-Eyes Mihawk, and Krieg attempts to take control of the Baratie.
As Nami steals the Going Merry, Mihawk has returned to finish the job, but Zoro challenges him to a duel in order to achieve his dream.
Mihawk leaves after defeating Zoro, so Krieg continues his invasion and has Pearl, one of his stronger crewmates, attack, and Sanji reveals his fighting skills. Meanwhile Johnny and Yosaku leave with Ussop and the wounded Zoro to go after Nami.
With Zeff held captive by Gin, Sanji has no choice but to take Pearl's hits, and he reflects on why Zeff means so much to him.
Gin finishes off Pearl, claiming that he wants to kill Sanji himself. Still wounded, Sanji faces Gin while Luffy attacks Don Krieg.
When Gin refuses to kill Sanji, Krieg uses a poison gas on him. Luffy seems to have the advantage in the fight until Krieg pulls out his explosive Battle Spear.
Even after taking several hits from the Battle Spear, Luffy refuses to give up.
After the battle, Gin decides to go back to the Grand Line with Krieg despite still being poisoned, and Sanji makes the difficult decision on whether to stay or to go with Luffy just as Yosaku comes back with news that he knows where Nami is.