Need your help finding a lost anime name.

Basically, it is about a guy who is part of the worst special forces division in his academy. He fights together with a pretty skilled I believe red-haired girl. One particular scene I can remember very clearly is when they invade a building and the MC is facing multiple enemies. They are laughing at him and mocking him for using a sword while they are all having guns, which makes him enraged and he later cuts a bullet in half with his sword. Only the mission operator sitting back in the base was able to cool him down from his anger by whispering a slight "onii-chan" into the microphone.

Well this is all I can really remember and I hope someone recognizes this random pieces of information that I gave XD.