Full Metal Panic?: Fumoffu (2003)

Sousuke's locked, loaded, and ready to attack which would be awesome if he was going into battle. But he's just going to high school, and all the qualities that make him a good soldier make him an amazingly awkward classmate. Poor Kaname knows that better than anyone, since Sousuke's her undercover bodyguard. The guy's supposed to protect Tessa too. But how top secret can he really be when he's sneaking around in a teddy bear suit, blowing up lockers, striking out with every girl in sight, and taking a mech to the hot springs? Sure, Sousuke's methods are a little intense, but high school's tough. Collateral damage is to be expected, right?