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Crystal Kay (Japanese: クリスタル・ケイ Kurisutaru Kei; born Crystal Kay Williams in Yokohama, Japan on February 26, 1986) is a Japanese singer.
Kay was the singer of ONE, the ending theme song of the eleventh Pokémon movie, Giratina and the Sky Warrior. The CD featuring this song was her 25th single. The film's producers had been considering Kay since she had sung "LOST CHILD" for the "Satorare" film in 2001.  She also provided the voice of Nurse Joy's Chansey in that film.