Ten years ago, humanity saw the lethal power of weapons unleashed by the Great War. To prevent a repeat disaster, governments around the world have turned to espionage to achieve their goals. In the Din Republic, Lily is a spirited young girl who dreams of becoming a spy and serving her country. Yet, she starts to question her skills, finding it hard to keep up in school. Her drive returns when she is given a chance to graduate provisionally by joining the spy unit Lamplight, which she gladly takes despite the mysterious nature of the offer. When Lily reaches her destination, she is startled to discover six other girls already there, each having dealt with their own school struggles. A mysterious man called Klaus soon shows up and explains they must take on an "Impossible Mission": to sneak into the Galgad Empire after only one month of training. Though doubtful, the girls finally agree to cooperate under Klaus' supervision—as this could be their sole opportunity to demonstrate their value as spies.