What is the name of this anime?

So, I watched it in my friend's dorm room, 4 or 5 years ago.

I think it is a spin-off anime.

But the point is there is this guy, he is like a secret agent, and he is protecting this girl. And they are just at school. But since he is a secret agent, while they are doing mundane things like going to the beach, he does the tasks over the top awesome, and he is a bit detached from the "normal" way to do things.