The young sergeant, Sagara Sousuke, and his comrades, Melissa Mao and Kurz Weber are given an unusual mission by the leaders of Mithrill, the military organization they work at. They are to become bodyguards of high school girl, Chidori Kaname, who apparently possesses unusual hidden knowledge, that can be the key to dramatic technological development. Sagara is signed up in Chidori's school, and hilarity ensues. The sergeant isn't used to peaceful life, constantly suspecting that every person is out to get him or the girl he's supposed to guard, that every cellphone is used to relay information between hostiles, every camera is used for spying and every car is rigged to explode, something which causes him to receive severe beatings from his classmates.
It all seems to be just fun and games, until a fated field trip, during which the plane they were on gets hijacked by terrorists. Sagara is surprised to recognize one of the enemy soldiers, who is apparently his thought-to-be-dead arch nemesis, and psychotic terrorist for hire, Gaul. Mithrill intervenes, and saves the class, while Sagara and his long time best friend, Weber rescue Chidori. It looks like they're in for a Bolivian Army ending, but Mithrill sends an unusual machine, the Arbalest, to aid them.
With Chidori knowing Sagara's secret, the two get closer to each other, and life is never the same again. Sagara is often called in for missions, while he also has his school duties to pay attention to. In the meantime, terrorists keep coming and war keeps on going all over the world. Not to mention Gaul keeps showing up just to prove that he cannot be killed.
Based on a series of novels written by Gato Shoji, Full Metal Panic is an anime series spanning 3 seasons. The first season, follows Sagara's life, the missions he must undertake and his conflict with Gaul who crosses his path on several occasions. The second season breaks away from the plot and focuses on the everyday school life, as well as Sagara's exploits as the mysterious mouse-like vigilante, Bonta kun, while introducing a few extra characters. The third season (also known as The Second Raid) introduces Mithrill's enemy, the terrorist organisation Amalgam, and their attempt to instigate a civil war in China. The series ends with many plot threads unresolved, but it's not likely the studio will continue it. I AM thinking about buying the books if I can.