Zero repeat forever - G. S. Prendergast

The 5th Wave meets Beauty and the Beast in this fast-paced and heart-stopping novel about an invasion of murderous creatures and one girl fighting for her life at the end of the world.

He has no voice or name, only a rank, Eighth. He doesn't know the details of the mission, only the directives that hum in his mind: Dart the humans. Leave them where they fall.
His job is to protect his Offside. Let her do the shooting.
Until a human kills her.

Sixteen-year-old Raven is at summer camp when the terrifying armored Nahx invade. Isolated in the wilderness, Raven and her fellow campers can only stay put. Await rescue. Raven doesn't like feeling helpless, but what choice does she have?

Then a Nahx kills her boyfriend.

Thrown together in a violent, unfamiliar world, Eighth and Raven should feel only hate and fear. But when Raven is injured, and Eighth deserts his unit, their survival comes to depend on trusting each other.