After their adventures in Alabasta, the crew come upon another deserted island and split up tasks amongst themselves. Chopper is left in charge of guarding the ship, and he reminisces about the day he first made the rumble ball and his first patient, Dr. Kureha, while spending some time with the newest crewmember: Nico Robin.

The Going Merry runs into several Marine ships in some fog, and the Straw Hats meet a trainee Marine chef named Tajiyo. Sanji helps him out of a bit of cooking trouble.

The crew stops on an island that's having its annual fireworks festival; Usopp meets a young fireworks-maker named Kodama and helps her achieve her dream.

Zoro has a flashback about the time when he first met Johnny and Yosaku, and faced off against Bandits and, Dick.

After escaping from several Marine ships, the Straw Hats land on an uncharted island and meet an old man named Zenny. Chopper finds out that, because of his bad heart, Zenny probably only has three days to live.

The Straw Hats help Zenny out, hoping to make his last days good ones; they learn about Zenny's past as a money lender, and his dream of becoming a pirate. But Zoro realizes that Zenny has outlived Chopper's predictions and so the straw hats decide that, after helping him finish his pirate ship, they will leave the island.

Zenny decides to follow his dream and become a pirate, despite his age. He helps the Straw Hats out of trouble with the Marines, and then they part ways.

On Ruluka Island, some of the Straw Hats make enemies of the Mayor and his men, who have placed high taxes on everything. Robin, Usopp, and Luffy meet Professor Henzo, who's doing research on the island's rainbow mist. When some of the mist shows up, Henzo borrows the Going Merry to go explore it.

The inside of the Rainbow Mist full of wrecked ships and treasure, and is guarded by five kids. The kids are actually friends of Henzo's that got lost in the mist over 50 years ago.

Henzo, his friends, and the others try to find a way out of the ship graveyard. Meanwhile, the Mayor and his men let the information about the Rainbow Mist slip to the remaining Straw Hats still on Ruluka.

Luffy accidentally propels himself and Rapanui to the end of the mist. Nami appears in the ship graveyard with a rowboat full of treasure and a string connected to the real world, which are both stolen by Wetton's subordinate. The Mayor uses the Rainbow Tower to make a bridge to the Rainbow Mist.

The Going Merry escapes from the Rainbow Mist, getting badly damaged on the way. The Mayor gets arrested by a bunch of powerful marines that turn out to be older versions of Henzo's friends, who were thrown 50 years into the past by the Rainbow Mist's collapse.