A group of pirates lead by Alvida plunder a ship, only to find a barrel which contains a strange boy named Luffy. Luffy is on a mission to find the legendary treasure "One Piece" and he befriends the ship's cabin-boy, Coby, who actually wants to become a marine officer. Luffy defeats Alvida and the two journey on in search of crewmates.
Luffy and Coby arrive at Shell Island, a Marine base. They meet the bounty hunter Roronoa Zoro, held under arrest by the infamous marine, Captain Morgan, and his son Helmeppo.
Luffy convinces Zoro to join his crew, but they must first defeat Captain Morgan. After freeing the island from Morgan's oppressive rule, Coby is accepted as a marine while the other two continue on their journey.
Out on the sea, Luffy almost loses his hat and reflects on his past, and how a pirate named Shanks influenced him. Afterwards, Luffy meets Nami, and Buggy the Clown's men.
In order to save herself and steal a map to the Grand Line, Nami tricks Luffy into allowing her to turn him over to Buggy.
Mohji and Richie show up for revenge after Buggy's humiliating defeat in the previous episode, and Luffy meets a small dog guarding his master's store, even though he knows that he is long dead.
Enraged by the actions of Buggy's crew, the city's mayor rushes to fight Buggy himself, but the Straw Hat Pirates come to his rescue. Zoro fights Cabaji, despite still being wounded from his previous encounter with Buggy, while Luffy faces the clown pirate himself and Nami searches for the map to the Grand Line.
Buggy's link to Shanks is revealed, and when he rips the straw hat Shanks gave Luffy, his rage knows no bounds. Who will win in this clash between Devil Fruit users?
Nami form an alliance becoming the navigator of the crew, but not a full member yet. They arrive in Syrup Village looking for a suitable ship. On this island they know the liar Usopp, who also has ties to the Shanx.
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 Pirates 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 Usopp 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.
The crew chases after Nami, who stole their ship, and Yosaku takes time during the trip to explain about Arlong and his Fishmen to Luffy and Sanji. Meanwhile, Usopp, Johnny, and Zoro arrive at the island Nami docked at.
Zoro is captured by the fishmen after Usopp and Johnny ditch him, and it's revealed that Nami was part of Arlong's crew the entire time. When a group of Fishmen attack Cocoyashi Village, Usopp comes to the rescue.
After Zoro escapes with Nami's help, she tries to prove her loyalty to the Arlong Pirates by appearing to kill Usopp. Meanwhile, Luffy's group finally arrives at the island.
Johnny tells the others about Nami killing Usopp, and Luffy does not believe them until Nami appears herself and confirms it. She tells them to stay out of her business and leave without her, but Luffy stubbornly decides to stay on the island. Usopp returns, revealing that Nami only pretended to kill him, and Nami's sister, Nojiko, starts to explain why Nami is acting the way she is.
Nojiko starts her story about Nami's childhood and their adopted mother, Bellemere. Despite being poor and none of them being related by blood, they had a happy life.
Nojiko continues her story, explaining how their life was ruined when the Arlong Pirates first took over the village.
When a marine officer under Arlong's pay confiscates all the money Nami stole over the years, in order to one day buy the village from Arlong, the villagers decide that enough is enough and fight back, despite Nami's pleads that they do not and that they'd all be killed. Upon seeing Nami's sorrow, the Straw Hats head for Arlong Park.
The Straw Hats face the Fishmen themselves as the villagers watch from the sidelines.
Arlong has trapped Luffy in the ocean and Zoro faces the six-sword wielding octopus Hatchan.
With Hatchan defeated, two of the fishmen battle Sanji and Usopp. Things look grim for Sanji as he attempts to face Kuroobi underwater, and Usopp gets the chance to prove that he too is a brave warrior.
Arlong's officers have been defeated, but Sanji and Zoro prove to be no match for Arlong in their current state. However, with Luffy finally free, he just may be able to defeat the "most wicked man in the East Blue". Meanwhile, Nami finally gathers the courage to face Arlong.
Luffy returns to the fight, and the battle with Arlong versus Luffy begins.
The battle spreads into Arlong Park itself and Arlong is no longer holding back.
Arlong's reign of terror is over, and no one has anything on their mind except to party. As the crew celebrates, Nami reflects on her hometown and decides to officially join the Straw Hat Pirates.
As a result of defeating Buggy, Krieg and Arlong, Luffy now has the highest bounty in all of East Blue. News quickly spreads to Shanks, who celebrates Luffy's arrival into the world of pirates by partying with Mihawk, despite already being severely hungover.
After his fight with Luffy, Buggy was sent flying to another island with several body parts missing. Thus, Buggy begins his journey to find his crew and his body parts, making some unlikely friends.
With Buggy assumed to be dead, his crew fights over who will be the new captain, only to be captured by a tribe of cannibals.
The crew arrives at the last large town before the entrance to the Grand Line--Loguetown, the place where Gold Roger was both born and executed, where they stock up on supplies and sightsee. As Luffy heads for the execution platform where Roger was killed, old enemies are searching for him.
While searching for new swords to replace the ones shattered by Mihawk, Zoro meets a woman named Tashigi, who looks exactly like an older Kuina, who then helps him look.
Usopp manages to anger the daughter of bounty hunter Daddy the Father, and finds his own life at stake. When Daddy discovers that Usopp is the son of Yasopp, the only man to beat him, he challenges him to a duel.
In order to win a rare fish, Sanji enters a cooking contest and faces a woman named Carmen.
Luffy arrives at the execution platform only to be caught in a trap by Buggy and Alvida.
Miraculously saved from death by an unnatural green gust and a lightning bolt to Buggy, the Straw Hats rush out of Loguetown, only for Zoro to be stopped by Tashigi and Luffy to be stopped by Captain Smoker.
On a stormy night a girl called Apis escapes from the Marines and arrives at Straw hat's ship, but the girl upon knowing that they are pirates begins to hide some of the reasons which she is being wanted by the Marines. As the Straw Hats escape from the Marines, they get caught in the Calm Belt.
After escaping the clutches of the Marine fleet, the Straw Hats soon find themselves in an equally dangerous predicament - stranded in the Calm Belt!
The Straw Hats want to return Apis's dragon to his nest, but the Marines have them surrounded. Looks like it's time for another daring escape!
Even for Nami, finding the dragon's lost island proves to be tougher than looking for a needle in a haystack - or at the bottom of the ocean.
Zoro is left fighting with Eric while Luffy and the gang run to the ship in order to get to Lost Island, but only find more problems.
At last Admiral Nelson has seen through the ambitions of Eric, but takes it a little too personally and now the mystical dragon's life is in danger.
With his last breath, Ryuuji calls all his fellow dragons, and the Lost Island re-surfaced. Meanwhile Luffy takes out Admiral Nelson and his gang.
After leaving Warship Island the Going Merry is now towards the Grand Line, and the crew now returns to the Great Adventure.