Returning to Jindai High School, Sergeant Sousuke Sagara safeguards the valuable war asset, Kaname Chidori, with a twist of awkwardness and danger due to his social ineptitude. Armed with an arsenal of unconventional solutions, Sousuke's antics disrupt the tranquil school routine Kaname craves, testing her role as student council vice president. Striving for balance, Sousuke occasionally adopts the guise of Bonta-kun, a popular amusement park character, which he upgrades into a quirky, but malfunctioning exoskeleton that amusingly only utters 'mofu.' Through their misadventures, Full Metal Panic? Fumoffu follows Kaname and Sousuke navigating the challenges of school life amidst their unintentional havoc.