One Piece: Defeat the Pirate Ganzack! (1998)

As the Straw Hat Pirates sail through the Grand Line, a sudden eruption of geysers beneath the Going Merry sends the crew flying over a nearby island. In the chaos, Chopper falls overboard and becomes separated from his friends. While Luffy and the others land on the far side of the island, Chopper finds himself hailed as the new king by the local animals. However, danger looms as a group of human “horn hunters” arrives. Their leader, Count Butler, is a violin-playing man who consumes horns to gain strength, and he seeks to devour the island’s greatest treasure to inherit immense power. Can Luffy and the crew stop Count Butler’s scheme and save the island? And will they be able to show Momambi that not all pirates are the villains he believes them to be?

The special takes place during the two year before the Straw Hats reunite on Sabody. Luffy is currently in Rusukaina training to get stronger to take on the New World. However the training is interrupted when Hancock's sisters, Marigold and Sandersonia, are kidnapped by the Byrnndi World, a pirate who was locked away on Level 6 of Impel Down but escaped during Luffy's invasion to save Ace, in order to lure Hancock to him and use her as a hostage against the World Government due to her Shichibukai status. Thus Luffy and Hancock head off to confront him and save Hancock's sisters.

The Straw Hats visit a recreational island, run by Baron Omatsuri, who asks them to complete a series of ordeals if they wish to stay on the island. Luffy accepts and the Straw Hats work together to complete them, but as the island's mysteries unfold, their lives and friendships are put to the test. It's up to Luffy to stop the Baron's plot and keep his crew together.

Desperate for cash, the Straw Hat Pirates enter a secret race between pirate crews known as the Dead End Competition. There, they must battle against powerful people, including the bounty hunter who wants to kill Gasparde and a climatic battle with Marine-turned-pirate Captain Gasparde.

From a brotherhood bound by three cups of sake, one brother’s story has yet to be told! Visiting Dressrosa under orders of the Revolutionary Army, Sabo’s top-secret mission derails when Doflamingo announces the grand prize for battling in the Colosseum. The tragedy at Marineford still weighing on his mind, Sabo reunites with his little brother to protect the promises they made with Ace. Now, they’ll fight in disguise for the Colosseum’s ultimate prize: Ace’s Flame-Flame Fruit.

After Nami steals the Going Merry, Roronoa Zoro, Usopp, and later Monkey D. Luffy and Sanji (along with Johnny and Yosaku) set after her and wind up in Cocoyasi Village, Nami's hometown ruled by the tyrannical fishman Arlong. It is here that Nami's past and true motives come to light.

A girl named Olga is pursued by both the World Government and a man named Mad Treasure, as she is the only one who knows the location of the Pure Gold, a substance that can buy the entire world. Olga ends up sailing with the Straw Hat Pirates, and they journey to find the Pure Gold on the lost island of Alchemi, which is located inside the stomach of a large angler fish named Bonbori.

The glittering Gran Tesoro, a city of entertainment beyond the laws of the government, is a sanctuary for the world’s most infamous pirates, Marines, and filthy rich millionaires. Drawn by dreams of hitting the jackpot, Captain Luffy and his crew sail straight for the gold. But behind the gilded curtains lies a powerful king whose deep pockets and deeper ambitions spell disaster for the Straw Hats and the New World alike.

There once was a pirate known as the Great Gold Pirate Woonan, who obtained almost one-third of the world's gold. Over the course of a few years, the pirate's existence faded, and a legend grew that he disappeared with his gold to a remote island, an island pirates continue to search for. Aboard the Going Merry, Luffy and his crew, starved and reckless, are robbed of their treasure. In an attempt to get it back, they wreck the getaway ship, guided by a young boy named Tobio, who's a captured part of El Drago's pirate crew. El Drago's love for gold has driven him to look for Woonan's island, and thanks to Woonan's treasure map, he finds it. During this time, Luffy's crew have been split up, and despite their own circumstances, they must find a way to stop El Drago from obtaining Woonan's gold.

The Straw Hats visits an island, known as Mecha Island, where a fisherman sings an old folk song about a Golden Crown. Searching for that mysterious treasure, they find a hidden entrance into the island. The island's leader, Ratchet, impressed with the find and in search of the Golden Crown himself, invites the crew to join him in his search and the crew along with Ratchet and his henchmen enter the cave. As it turns out, the islands true form, is that of a giant turtle. Ratchet, who had known this all along, uses his mechanical castle to take control of the turtle, in order to use it, to take over the world. Now the Straw Hats have to stop not only Ratchet, but also the helpless turtle, from crashing into a nearby island.