Alvida liderliğindeki bir grup korsan bir gemiyi yağmalar, ancak içinden Luffy adında tuhaf bir çocuk çıkan bir fıçı bulurlar. Luffy, efsanevi hazine "One Piece"i bulma görevindedir ve geminin aslında bir deniz subayı olmak isteyen miçosu Coby ile arkadaş olur. Luffy, Alvida'yı mağlup eder ve ikisi mürettebat arkadaşı aramak üzere yolculuklarına devam ederler.

Luffy ve Coby, bir Denizci üssü olan Shell Adası'na varırlar. Burada, kötü şöhretli denizci Yüzbaşı Morgan ve oğlu Helmeppo tarafından tutuklu bulunan ödül avcısı Roronoa Zoro ile tanışırlar.

Luffy, Zoro'yu tayfasına katılması için ikna eder, ancak önce Yüzbaşı Morgan'ı yenmeleri gerekmektedir. Adayı Morgan'ın baskıcı yönetiminden kurtardıktan sonra, Coby denizci olarak kabul edilirken diğer ikisi yolculuklarına devam eder.

Açık denizde, Luffy neredeyse şapkasını kaybeder ve geçmişini, Shanks adındaki bir korsanın onu nasıl etkilediğini düşünür. Sonrasında Luffy, Nami ve Palyaço Buggy'nin adamlarıyla tanışır.

Kendini kurtarmak ve Grand Line'a giden bir haritayı çalmak için Nami, Luffy'yi kandırarak onu Buggy'ye teslim eder.

Önceki bölümde Buggy'nin küçük düşürücü yenilgisinin ardından Mohji ve Richie intikam için ortaya çıkar. Luffy ise sahibinin çoktan ölmüş olduğunu bilmesine rağmen onun dükkanını koruyan küçük bir köpekle tanışır.

Buggy'nin tayfasının yaptıklarına öfkelenen şehrin belediye başkanı, Buggy ile bizzat savaşmaya koşar ancak Hasır Şapka Korsanları onu kurtarmaya gelir. Zoro, Buggy ile olan önceki karşılaşmasından dolayı hala yaralı olmasına rağmen Cabaji ile dövüşürken, Luffy palyaço korsanın kendisiyle yüzleşir ve Nami de Grand Line haritasını arar.

Buggy'nin Shanks ile olan bağlantısı ortaya çıkar ve Shanks'in Luffy'ye verdiği hasır şapkayı yırttığında, Luffy'nin öfkesi sınır tanımaz. Şeytan Meyvesi kullanıcıları arasındaki bu çarpışmayı kim kazanacak?

Nami, tayfanın rotacısı olmak üzere bir ittifak kurar ancak henüz tam üye değildir. Uygun bir gemi arayışıyla Şurup Köyü'ne varırlar. Bu adada, aynı zamanda Shanks ile bağları olan yalancı Usopp ile tanışırlar.

Usopp, zengin arkadaşı Kaya'yı Hasır Şapkalar'a bir gemi vermesi için ikna etmeye çalışırken, Kaya'nın hizmetkarı Klahadore tarafından ondan uzak durması söylenir. Ancak daha sonra Usopp ve Luffy, Klahadore'u tuhaf bir adamla konuşurken gördüklerinde, Kaya'yı öldürmeye yönelik bir komployu öğrenirler.

Kaptan Kuro'nun şeytani planını öğrendikten sonra Usopp, Kaya'yı uyarmak için köye geri koşar ancak yıllardır söylediği yalanlar yüzünden kimsenin ona inanmadığını fark eder.

Usopp, köye hiçbir korsanın ulaşmamasını sağlayarak korsanların saldırdığı hikayesini bir yalan olarak sürdürmeye karar verir. Luffy, Zoro, Nami ve Usopp daha sonra Kara Kedi Korsanları'nı durdurmaya çalışır.

Hasır Şapkalar, karşılarındaki Kara Kedi Korsanları'nın çoğunu alt etmeyi başarır, bu yüzden Jango, Miyavban Kardeşler'e saldırmalarını emreder. Bu sırada, Jango tarafından hipnotize edilen Luffy, Kara Kedi Korsanları'nın gemisinin yıkılmış direğinin altında sıkışıp kalır.

Kaptan Kuro'nun bizzat olay yerine gelmesiyle ve Zoro'nun savaşamayacak kadar yaralı, Luffy'nin hareket edemez durumda ve diğer ikisinin de onunla başa çıkamayacak kadar zayıf olmasıyla durum umutsuz görünür. Ancak, Kuro ile pazarlık yapmak için Kaya'nın kendisi ortaya çıkar.

Luffy ve Kuro dövüşlerine başlarken, Zoro ve Buchi (Miyavban Kardeşler'den) bir kez daha karşı karşıya gelir. Usopp, Usopp Korsanları'na Kaya ile birlikte kaçmalarını emreder, ancak Jango onların peşine düşer. Bir geri dönüş (flashback), Kaptan Kuro'nun Kaptan Morgan ile birlikte kendi ölümünü nasıl tezgahladığını ve nasıl Kaya'nın hizmetkarı olduğunu ortaya çıkarır.

Luffy ve Kuro arasındaki dövüş sona yaklaşırken, Usopp Korsanları Jango'dan kaçınmak için ellerinden geleni yaparlar.

Kuro'nun nihai saldırısı "Şakuşi", alandaki dost veya düşman ayırt etmeksizin her şeye saldırır ve Luffy, Kuro'nun kendi tayfasına olan saygısızlığı karşısında öfkelenir. Luffy'nin kararlılığı, Kuro'nun saf hızının üstesinden gelebilecek mi?

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.

n 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.

The Calm Belt is revealed to have no winds or currents as well as being the home of many giant sea kings. Apis forms a plan with Luffy's help and escapes the sea kings by riding with one's sneeze. Later, the crew reaches Warship Island, where they listen to the soporific story of the island's creation. After following Apis into a cave where a dragon is hidden, Luffy and Nami find the reason why Apis is being chased.

Now that the crew is informed about the reasons for which Apis was followed, they hurry to escape the island so Ryuuji could be saved, but they meet with a foe that wants Ryuuji to himself. Zoro and Usopp bring the ship to a thin rock at the side while Nami and Apis get Ryuuji onto a cart. Luffy and Sanji fight the Marines to buy time for all preparations. In the end, the ship pulls the cart away on the search for Lost Island.

After arriving to what might seemed as the Lost Island the Straw hats where looking for, they find an old Temple with paintings that might indicate where the Lost Island really is, and also Eric who has been following them throughout the sea.

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.