Sagara Sousuke stands out among his high school peers due to his military quirks, from reading enthusiast magazines to casually carrying grenades. Despite being labeled as a military fanatic by his classmates, Chidori Kaname sees a deeper layer to his persona. During a hijacking incident on a school trip, Kaname's suspicions are validated as Sousuke reveals his true identity as a skilled mercenary pilot of mechs, assigned to safeguard her.