Yoshino Reiji is an ordinary student living at Tsukiyomijima Island. One day, an abnormal predicament struck him, and a beautiful girl named Sakura appears in front of him, saving his life. She tells him he is the Missing Number 13, and she is his strategy destruction magic weapon (a.k.a. magic). Both Reiji and Sakura are forced to fight against the other twelve Mahoutsukai in a battle royale-style ritual. To protect his peaceful everyday life, Reiji casts himself into battle.