Quick recap
A 2016 TV special, non-canon, leading into One Piece Film: Gold. The Straw Hats meet Olga, a girl who escaped the island of Alchemi, once known for its metalwork and the priceless Pure Gold, but missing for two hundred years. The Marines chase Olga for the treasure, and Gild Tesoro hires the treasure hunter Mad Treasure to catch her. The crew joins her search for the Pure Gold, unaware that Olga plans to use them to get rich. The special leaves Tesoro's name hanging, setting the stage for the film.
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