One Piece: Baron Omatsuri and the Secret Island (2005) Anime Watch

Luffy finds a glass bottle floating in the water with a map to Omatsuri Island and a notice saying he's been chosen among the 100,000,000 pirates of Grand Line to go there for adventure. Of course everyone smells something fishy except the only person that counts, Luffy.

So they go. It would appear that there's nothing special about the island but suddenly a magical theme park, parade and chorus all appear before their eyes welcoming them. At the center of it all is the Baron Omatsuri. What secrets and dangers wait for them on the island?