The series follows Taiyou Asano, a high school student who becomes entangled with the Yozakura family, a clan of elite spies. After the death of his own family, Taiyou finds companionship in his childhood friend, Mutsumi Yozakura. However, her life is constantly in danger due to her family's profession. To protect Mutsumi from her overprotective older brother, Kyoichiro, and other threats, Taiyou must marry her and officially become a member of the Yozakura family. He then begins rigorous training to become a spy himself, navigating dangerous missions while developing his relationship with Mutsumi and learning the secrets of the spy world.