A band of pirates led by Alvida plundered a ship, only to find a barrel which contains a strange boy named Luffy. Luffy is on a quest to find the legendary treasure "One Piece" and he befriends the ship's cabin-boy, Koby, who actually wants to become a marine officer. Luffy defeats Alvida and the two journey on in search of crewmates.

Luffy convinces Zoro to join his crew, but they must first defeat Captain Morgan. After freeing the island from Morgan's oppressive rule, Koby is accepted as a marine while the other two continue on their journey.