Sergeant Sousuke Sagara returns to Jindai High School to protect Kaname Chidori, a valuable war asset. However, his lack of social skills and real-world experience cause comical and hazardous situations that disrupt Kaname's desire for peace. To counter perceived threats, Sousuke brings a cache of weapons to school, while Kaname strives to fulfill her duties as the student council VP and keep Sousuke in line. At times, Sousuke dons a Bonta-kun costume, a beloved amusement park character, and transforms it into a high-tech exoskeleton that only produces nonsensical "mofu" sounds, using his technical expertise. Full Metal Panic? Fumoffu chronicles Kaname and Sousuke's efforts to lead a normal school life while struggling with the chaos they inadvertently create.