
The Earth is in grave danger: Powerful inhabitants of the parallel world Cephiro have appeared in Tokyo and are anything but well-disposed towards our world. All humans have suddenly disappeared without a trace. Only the three friends Ikaru, Umi, and Fuu remain in Tokyo for mysterious reasons and must fight for the future of the Earth with legendary robots. But the battle cannot be won by force alone.
Hikaru, Umi, and Fuu are three fifteen-year-olds from Tokyo in their final year of middle school. The three girls are very close friends and once, under the cherry tree in their school garden, they swore to each other never to be separated, for any reason. Now, however, as the year draws to a close, things seem to be going against their wishes: after graduation, they will be going their separate ways. One day, while Hikaru is under the cherry tree, an earthquake shakes her, and at that moment, a funny white rabbit-like elf, Mokona, falls from the tree, seemingly visible only to her. At the same time, strange monsters begin appearing in Tokyo, intent on destroying the city. The three remaining girls, the only ones who haven't disappeared, meet Clef, who helps them become Magic Knights to defend the Earth from invaders. To finally defeat the enemies, who come from a world called Cefiro, they must awaken the three Mashin that lie deep within the Earth.
Hikaru, Umi, and Fuu are already friends at school in Tokyo. Suddenly a strange creature, Mokona, appears before them. Along with Mokona, monsters and wizards from Cephiro begin to invade Earth (Tokyo).