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.

The Straw Hat Pirates landed at Asuka Island, home of the most valuable sword in the world: The Seven Star Sword. Which was said to curse anyone who takes it in possession. When they got back to the Going Merry, they discovered that Zoro is missing from his guard duty. Before they could plan out a search party to relocate him. Luffy and friends escape from the port as Marines were on their tail. They found a new place to dock, which is near a village. Whose job is to keep the Seven Star Sword sealed. Soon it was attacked by the Marines, and among them is Zoro. Luffy and the others don't know why he's helping out the Marines. But it all comes to conclusion when Luffy encounters Saga: Zoro's childhood friend from Swordsman training.

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.