From the video description:

<Introduction>

While on a field trip to Tokyo Tower, Hikaru Shidou, Umi Ryūzaki, and Fū Hououji are suddenly summoned to the alternate world of “Cephiro.”

There, the three learn that Princess Emeraude — who has long protected the peace and order of “Cephiro” through the power of prayer — has been taken captive, plunging the world into crisis.

Summoned by Princess Emeraude to save “Cephiro,” will these three girls truly become the legendary “Magic Knights” and save the princess and the world!?

Official Site: https://rayearth-anime.com/