Here's the short story description of Rainbow Knights basing it from a part of the original synopsis that I could recall.

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STORY DESCRIPTION: Seven girls ー Konami, Mari, Miiko, Chifuyu, Azami, Chihomi and Maiya ー had their lives changed all of a sudden when each of them became chosen to wield seven powers ー fire, light, wind, earth, water, sound, and ice. Guided by the Chief Fairy Angel named Rainne, they were soon given the immense task to battle the threat coming from the Olgox who made it their mission to conquer both the Earth and the world of Ralvalea. The girls were able to do such a feat by becoming the legendary seven-colored Angel Knights of the ancient Ralvalea, the Rainbow Knights!