The story is set in a distant future where Japan is divided into feudal territories and conquered by other countries. There is a floating city named Musashi that is composed of eight ships in the skies. A war that will determine the fate of the world will be fought by students on the Musashi.
A series of humorous shorts supplementing the Kyoukaisenjou no Horizon anime.

In the far future, humans abandon the devastated Earth and move to the upper world "Tenjo". But Tenjo and the law of causation collapse by a war and humans returns to the Earth, which has turns into an inhabitable planet except for Shinshu area. Shinshu is too small to accommodate all the humans, so they duplicate the area and create "Juso Sekai". In order to rebuild Tenjo and the law of causation, the returned humans start reproduction of history from B.C. 10,000. When the reproduction completes until A.D. 1413, a war breaks out in Shinshu and Juso Sekai falls onto the original world. The humans living in Juso Sekai lose their land and invade the original world. People in Shinshu surrender and is divided by the invaders from Juso Sekai. They try to resume the history reproduction from A.D.1457, but the update of history terminates in A.D.1648. A rumor of apocalypse begins to spread around the world.
- Wikipedia

The earth is ruled by the Black Witch.

The Black Witch was sealed in the moon and can only be judged once a decade on the night of Hexennacht. The ones who can fight the Black Witch are the chosen magical girls who have won their battles. Horinouchi Mitsuru, the Eastern Japan representative who aims to be the strongest, happens across a girl with strange power who says her name is Kagami Kagami.

The girls "clash"!

To save the world with their own power!!