Full Metal Panic!

A secret admirer leaves a love letter in Sousuke's shoe locker. Instead of finding the letter, he deduces that his locker was tampered with and promptly blows it up. From its fragments, Sousuke misinterprets the letter as a death threat and confronts his "stalker". Sousuke forgets Kaname's notes at home, and they make a frantic dash to retrieve them and return before lunchtime ends. Despite their tardiness, they find out that the notes were not needed since their teacher coincidentally fell sick.