Full Metal Panic!: Tanpenshuu

A high school student with unusual habits, Sagara Sousuke reads military publications, uses formal responses, and carries grenades to class. While his classmates dismiss him as a military obsessive, Chidori Kaname suspects there is more to him. During a school trip, when their plane is hijacked, Kaname's intuition proves right—Sousuke is a skilled mercenary who pilots mechs and is assigned to keep her safe.