Ruluka Island Arc

This is the fourth filler arc of the anime and has no basis in the manga. Its alternate title comes from the eerie Rainbow Mist phenomenon at its center. The segment is notable mainly as the last stretch of the series handled by the 4Kids dub.

The plot revolves around the island of Ruluka, a community squeezed dry by a corrupt mayor, and a scientist obsessed with the mysterious mist that surrounds the region.

The Going Merry is pursued by a small Marine flotilla under Lieutenant Commander Rapanui Pasqua, and the crew slips away when the officer clumsily sinks one of his own ships. They reach Ruluka, where a former pirate now governing as mayor, Wetton, overtaxes the residents to fund a grand Rainbow Tower. A researcher named Henzo, bankrolled by Wetton, studies the surrounding Rainbow Mist.

Most of the crew, aside from Sanji, Nami, and Chopper, becomes caught inside the mist while aboard the Merry. Within it they find a group of children who have been stranded there for many years, untouched by the passage of time. The crew eventually discovers a way out, but once back in the open the children cannot be located.

When the Marines arrive to make arrests, they explain there is no space aboard their vessel because Wetton and his gang have already been locked up. With the corrupt regime toppled, the Straw Hats depart the island, just in time to witness a ship plummeting out of the sky.

Being the final arc the 4Kids dub produced, several edits were applied, including recolored firearms, censored numerals in the Rainbow Mist books, a renamed location, and an accent change for one character. In the anime continuity this arc also depicts the Going Merry's gradual structural decline, since the ship is blasted out of the mist with such force that its figurehead breaks and a mast collapses before repairs are made on Ruluka.

The falling ship glimpsed at the close leads directly into the Jaya arc. Later canon involving time travel in Wano creates a minor inconsistency, since the crew acts surprised by the concept despite having encountered people from the past inside the Rainbow Mist here.