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The crystal mark of the People activating a sealed door
The People of the Water (Japanese: 水の民 People in the Water) are an ancient tribal society in the Pokémon world that was mentioned in Pokémon Ranger and the Temple of the Sea. Very little is known of their culture or their civilization.
As the name implies, the People of the Water were connected to the ocean, either living near or in it. They are apparently an almost extinct clan, with Lizabeth, Ship, and Lizabeth's parents Kyle and Meredith as the only known remaining descendants. They are characterized as having dark skin color and various shades of blue or black hair.
The People of the Water possessed advanced technology, having constructed the Sea Crown and Samiya the Sea Temple. Special crystals they own can activate these technologies, which range from opening doors to keeping the Sea Temple from sinking. During the events of the movie, May was given a crystal mark from Lizabeth.
The Phantom appears to be very knowledgeable about the People of the Water and even obtained one of their special crystals prior to the movie.
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