‘Magic Knight Rayearth’
Magic Knight Rayearth begins when three junior high school girls hear a voice asking them to save a world called Cephiro. The voice belongs to Princess Emeraude, the Pillar whose will maintains the peace of this magical world where belief is power. But the peace in Cephiro is now threatened as Princess Emeraude is imprisoned and monsters begin to invade the land. With her last bit of strength, the princess summons forth the three girls destined to become the Magic Knights in the hopes of saving her world.
Descriptions taken from AniDB.net