When I was in highschool I found a manga online and I can't remember the name of it.

The basic storyline (from what I remember) is that there is a school kid that leads a pathetic life and he isn't very strong or smart, but he has a twist on his life that he knows of. Whenever there is a girl in danger he gains almost superhuman strength, intellect,and agility and do almost anything. The first book (from what I remember) starts out with him telling his back story and shows his life right before some kind of secret agent (or assassin?) girl shows up and I think she tries to kill him, but at that time someone else terrorises the school and his ability kicks in and he saves her.

If anyone knows of this Manga, can you please tell me the name?

Sounds a lot like Hidan no Aria. Could that possibly be it?