An orphaned girl named Blue has always dreamed of joining the ranks of the noble Angels, servants of the floating palace who protect the Quartz Kingdom against demons. Yet, Blue is not like the other children at the orphanage. Where their fledgling angel wings are downy white, Blue's are pitch black, giving rise to whispers that she is cursed.

One day, the orphanage comes under attack by a host of demons. Angels swoop down from the palace to drive the demons back, but Blue watches in horror as they are cut down one after another. Just when all seems lost, Blue feels a dark power welling up inside of her. It may be enough to avenge her friends...but will the cost prove too great?