A new mission is assigned to Sousuke Sagara, a member of the anti-terrorist organization Mithril: protect a high school girl named Kaname Chidori, who lives in Japan. To stay close to her, Sousuke enrolls at her school as a student. However, having been raised as a soldier from a young age, he has little understanding of normal everyday life—leading to one misunderstanding and chaotic situation after another. What could possibly go wrong?