Breach

A world has crumbled and it's up to a team of soldiers to save them, can they manage or will it be like it always has and the vampires will rule them? What happens when one of their best soldiers turns out to be part enemy, will they use her in the fight or kill her?
This is an attack on titan based book, it's about a world that's fallen prey to an era where Vampires rule and the humans are trying to take back their world.