Little East Blue Arc

The Little East Blue Arc is a special anime-only arc consisting of four episodes, which is meant to lead into the One Piece Film: Strong World.

Summary
The arc begins twenty years in the past when Shiki manages to break his way out of Impel Down by cutting off his legs. He then uses his Devil Fruit power to escape into the air. The story then moves to present day, a submarine carrying a mariachi-style band of pirates known as the Amigo Pirates is shown making its way through the ocean. The leaders of the bunch, Largo and his brother Corto, are given the offer to join Shiki's assembly. However, they must fulfill a certain condition.

Meanwhile, the Straw Hat Pirates are fishing, trying to refill their rations when they are attacked by a large horned beetle. After a brief skirmish, the beetle takes Luffy, along with Usopp, Sanji, and Zoro, to a nearby island. There they meet its owner, Yoko, who dubs the beetle "Boss" all the while showing a notable disdain for Luffy, as he is a pirate. Soon, the rest of the island's residents make themselves known, revealing that they actually know of the Straw Hats and their exploits. They lead them back their village, mentioning Yoko's past in the process (her father was a Marine who had helped protect the village, but was killed while defending it from pirates, hence her hatred of them). Once the group reaches their destination, they find the whole town modeled after East Blue, it is even named "Little East Blue". Usopp soon calls Nami on the Den Den Mushi, stating that the villagers wish to meet her. She obliges, hopping on her sky waver and heading toward the island. Meanwhile, the Amigo Pirates are closing in on the island as well, aiming to capture Boss since he is a runaway from Shiki's hideout.

Luffy, Zoro, Usopp and Sanji look around a bit, visiting the replicas of their respective homes as the villagers show them around. All the while, Yoko spies on them, continuing to show her disapproval of their presence. Nami meanwhile meets a few fans of hers, all boys, who show her a statue they carved using her bounty poster as reference (as well as also intentionally making her naked). Nami is not amused by the shrine. Eventually the town throws a banquet for the Straw Hats, to which Luffy stuffs himself beyond proportion. However in the midst of the celebration, Corto and the Amigo Pirates appear and crash the party demanding Boss. When the citizens refuse, the Amigos prepare to attack only to be taken down by Zoro, Sanji and Luffy. Just as Luffy is about to finish Corto, Largo suddenly appears and blindsides Luffy, with a net attack he suddenly shoots out of his hands that traps the Straw Hat captain in a spiked net, which pokes and scratches at him with every movement.

Largo then reveals he has eaten the Ami Ami no Mi and can make different nets out anything he eats, as he had done with Luffy's net after eating a hammer. Zoro and Sanji attempt to attack Largo themselves but he creates different nets for them and captures them as well before stringing all three Straw Hats up on a tree. Largo and Corto once again demand Boss or otherwise they would exterminate the town. Boss suddenly appears and, not wanting Little East Blue to be destroyed, agrees to give himself up. Just as he is about to fly into a cage Largo made for him, Luffy manages to tear open his net and punches him to the ground, angrily reminding him of their planned rematch. It is at this point that Boss begins his molting process. Once done he burns the nets holding Luffy, Sanji and Zoro who, once free, ready themselves for a final battle against the Amigo Pirates.

Luffy activates Gear Second and with some help from Sanji, punches Largo deep into the forest. He then chases him through the forest to the shore where they continue their fight, while Nami, Zoro, Sanji, Usopp, and the citizens of Little East Blue along with Boss take care of Corto and his men. Back at the shore, Largo uses his Ami Ami no Mi powers to turn his body into a net and captures Luffy inside himself. Luffy, however, uses Hone Fusen to tear the net, and then uses Gomu Gomu no Gigant Pistol to defeat him; slamming him into his own submarine and deep into the water. In the aftermath, Luffy and Boss have their rematch till both have tired themselves out ending the battle in a tie. Yoko, with some help from Nami, comes to learn that not all pirates are bad after seeing the Straw Hats willingly defend Boss and Little East Blue. Largo, Corto, and the Amigo Pirates are captured by the citizens of Little East Blue and put into a cage that Franky had originally made for Boss. With that, the Straw Hats sail on with Luffy promising Boss and Yoko that he will return someday. Meanwhile, Shiki is informed of the Amigo Pirates' failure to capture Boss (unaware of the Straw Hats' interference), but he casually explains that "one escapee does not affect the execution of my plan at all" as he view monitors of various animals with glowing eyes. Shiki then announces that the time to set his plan into action has begun.

Trivia

 * This is the first arc that is made to set up a movie. The second is the Z's Ambition Arc, for One Piece Film: Z.