I really want to find this anime, i remember i were watching it and i loved it
so here i go..

there was a boy who joined a school, not school like we did/do go to but it was some kind of millitary school its is fantasy anime, but later on everyone realised that he`s not a beginner that is just trying to learn battle abilitys but thats he is already really excelent solidier, there were competitions agains other team when who showed he`s true power, and later on in last episodes that town was attacked by monsters, some kind of bugs, and he was the main character who was fighting against them, and they couldnt go outside of town without masks so they could breath,, there were like 20+ episodes i think.

EDIT: main character was blind i think. and in the first episode he saved a girl from something i really dont remember, something falling i think.