this new manga came out a few months ago..it's name is Claymore.
It talks about these people, Claymore, which hunt down the Yoma's, some kind of monsters. Clea is one of these people, which has to go to a village and kill all these demons. After that she starts travelling with this boy called Raki, the only survivor, and we start discovering about Clea's past.
Probably the description wasn't very good...but I hope it was clear enough.