Three young girls, Hikaru, Umi, and Fuu, are transported to a magical world called Cephiro during a field trip to Tokyo Tower. They are soon greeted by Master Mage Clef, who explains to them that they have been summoned to become the Legendary Magic Knights and save Cephiro. The girls are less than enthusiastic about this idea, and only want to return home. Clef further explains that they must seek out the three Rune Gods to help them fight. He bestows armor and magical powers to each of them. They learn from Clef that High Priest Zagato has kidnapped the Pillar of Cephiro, Princess Emeraude. The Pillar of Cephiro has the sole responsibility of keeping Cephiro alive and in balance with her prayers. Without Princess Emeraude, Cephiro would fall into ruin. Hikaru, Umi, and Fuu must fight off Zagato's henchman and find the Rune Gods if they ever want to get back home. They soon learn that friendship and loyalty are the only things they can rely on in the crumbling Cephiro.
(Source: Anime News Network)
— Description from AniList community (anilist.co).
