Attack on Titan

Humanity has retreated to a giant city surrounded by enormous walls that protect them from the Titans, monstrous humanoid creatures who devour humans seemingly without reason. Eren Yeager, a boy that lives near the outermost wall, vows to rid the world of the Titans after they suddenly break through the wall and destroy his home, killing almost everyone in his town. He joins the Scout Regiment, an elite military group that fights the Titans, and sets out on a journey to uncover the mysteries of the Titans and humanity itself.