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

Storyline:
The Straw Hats visit a recreational island, run by Baron Omatsuri, who asks them to complete a series of ordeals if they wish to stay on the island. Luffy accepts and the Straw Hats work together to complete them, but as the island's mysteries unfold, their lives and friendships are put to the test. It's up to Luffy to stop the Baron's plot and keep his crew together.