FULL METAL PANIC! (Furumetaru Panikku!), based on the light novels by Shouji Gatou with art by Retsu Tateo. First published in 2000 and first published in North America in 2003.
PLOT:
Kaname Chidori is a popular, smart young girl who keeps busy with her duties as class representative. Everything would be perfectly normal for her if not for the new boy in class: Sousuke Sagara. As far as she knows, he's a weird military otaku who follows her everywhere and treats everything like a major threat. What she doesn't know is that Sousuke isn't just some gun nut, but an actual sergeant for the secret military organization MITHRIL. He and his teammates believe Kaname possesses a strange power that malicious forces want to exploit for their own purpose, and he is determined to protect her at all costs.