Detective Conan: Jolly Roger in the Deep Azure(2007)

Overview:

The Isle of Koumi, a beautiful island in the Pacific Ocean. On the island, people pass an old legend down from generation to generation that there was the Seabed Palace, an ancient ruin at the bottom of the sea, where the treasure of female pirates Anne Bonny and Mary Reed was left. When Conan and his friends visit Koumi while on vacation, they meet some suspicious treasure hunters.