The students of St. Cerise Academy are all busy preparing for the 100th school festival, and both Minazuki Haruka and Kannazuki Aoi are putting a lot of effort into their rehearsals for the stage performance Twin Angel Show.

Some days before the festival, a certain book is stolen from within the Academy Chapel. Following that, Haruka and Aoi become aware of the existence of a letter, a proclamation of war, issued by someone calling himself the Baron of the 4th Dimension.