Full Metal Panic!

Kaname Chidori stands as one of the most popular students at her high school, but the danger she faces comes from her growing off-campus notoriety. Unknown to her, terrorists are plotting her abduction, convinced she possesses the rare and coveted abilities of 'the Whispered.' Enter Sousuke Sagara, a fearless operator from the clandestine counter-terrorist organization Mithril, who goes undercover at Kaname's school to guard her. An ace pilot in the cockpit of an Arm Slave mech, he soon learns that no amount of battlefield training can prepare him for the warzone that is high school.