Well....there are these creatures known as Grimm that can cause a lot of damage and hurt people, so there are Hunters and Huntresses who protect people. They started out mostly with going to school to learn to be a Huntress to fight the Grimm, but then it turned out there's this plot by someone who does't care who gets hurt or who dies, just her agenda, so after the school was closed because of an attack, its become more of a quest or mission to stop her from hurting more people.