One Piece: Mega Mecha Soldier of Karakuri Castle is an anime film that premiered in spring 2006, produced by Toei Animation.

About the production: the story comes from an original script, the film runs about 94 minutes and its current status is "finished".

Its main genres are adventure, comedy and fantasy, with themes such as Pirates, Shounen, Ensemble Cast and Robots.

On AniList, One Piece: Mega Mecha Soldier of Karakuri Castle has an average score of 68%, a good score, and appears on 20,050 users' lists.

The franchise continues in or follows from: ONE PIECE THE MOVIE: Omatsuri Danshaku to Himitsu no Shima and ONE PIECE: Episode of Alabasta - Sabaku no Oujo to Kaizoku-tachi.

The crew salvages a treasure chest from a sinking wreck, but inside turns out to be an old lady hiding. To get the Straw Hat Pirates to take her home, she promises them the treasure of a golden crown on her island, Mecha Island. When they arrive, their ship is first attacked by the lord of the island. But later he decides to use the pirates to help him solve the riddle of the Golden Crown. (Source: Anime News Network)

Official synopsis from AniList.