When humanity discovered an alternate dimension filled with magical and mythical beings, the world as we knew it would never be the same. Humanity soon learned to harness these extra-dimensional forces and summon mystical beings into their midst through the power of "summoners." Years later, fifteen-year-old Kazuki Hayashizaki is chosen to be the first male summoner. His attendance at an all-female summoner school is met with much opposition, especially from his sister, a magical swordsman whose task is to guard summoners. Now she finds herself in an inferior position to her brother Kazuki, and will stop at nothing to thwart him.