One Piece S05 E139 Legend of the Rainbow Mist! Old Man Henzo of Luluka Island!

"Set sail for One Piece!"

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.