Full Metal Panic! (2002)

S2E1 The Man from the South / A Fruitless Lunchtime

A mysterious admirer slips a love letter into Sousuke's shoe locker, but when he discovers his locker has been messed with, he reacts by blowing it up. In the aftermath, he mistakenly interprets the remnants of the letter as a threat and goes after his supposed "stalker." Meanwhile, Sousuke leaves Kaname’s notes at home, prompting a hurried race to get them back before lunch wraps up. However, upon their arrival, they learn that the notes weren't necessary after all, as their teacher has unexpectedly fallen ill.