It all started with a legend passed down from the People of the Water - Somewhere in this world, there is a Sea Temple created by the People of the Water. The Sea Temple contains a hidden treasure called the Sea Crown, but no one has ever seen the Sea Crown, or even the Sea Temple, because the temple is protected by a secret mechanism. The temple drifts through a vast ocean undetected, waiting - waiting... Ash and Pikachu meet Lizabeth, a descendant of the People of the Water, and learn about the legend. They also meet Jackie, a Pokémon Ranger on a secret mission to protect a Manaphy egg (Manaphy is mysteriously known as The Prince of the Sea) and find the Sea Temple as well. The Phantom plans to obtain the Sea Crown and take over the world - but first he needs the Manaphy egg. Now Lizabeth and Ash must help Jackie protect the egg and stop the nefarious pirate.
—asianwiki