Until its use in conflict, magic was abundant and improved the lives of all people. To put a stop to the turmoil, seven of the most powerful wizards sacrificed their lives to imprison all magic. Almost a thousand years later, their magical seal Magiaconatus holds Granbelm, a monthly series of battles to decide who among its participants is deserving of the title of Princeps, the one genuine magician. Mangetsu Kohinata, a high school student, is unexpectedly taken to an illusionary realm where six magicians are competing in Granbelm on the night of a full moon. Mangetsu is attacked by two mages after being mistaken for an enemy mage, until she is saved by Shingetsu Ernesta Fukami and her Armanox Viola Katze.