Twin Princess of Wonder Planet(2005)

Twin Princess of Wonder Planet is an anime series set on a hollow world where seven kingdoms depend on the Sun's Blessing from a central sun for survival. When the sun's light begins to fade, threatening all life on the Mysterious Planet, twin princesses Fine and Rein of the Sun Kingdom must act. Blessed with the magic of the Prominence, the sisters embark on a quest to restore the sun's power before darkness consumes their world. The series blends fantasy adventure with themes of sisterhood and responsibility as the princesses navigate political intrigue and magical challenges across the seven kingdoms.