Attack on Titan

Attack on Titan is set in a world where humanity lives inside cities surrounded by enormous Walls that protect them from Titans, gigantic humanoid creatures who devour humans seemingly without reason. The story centers around Eren Jaeger and his childhood friends Mikasa Ackermann and Armin Arlelt whose lives are changed forever after the appearance of a Colossal Titan, which brings about the destruction of their home town and the death of Eren's mother. Vowing revenge and to reclaim the world from the Titans, Eren, Mikasa, and Armin join the Scout Regiment, an elite group of soldiers who fight Titans outside the Walls.

Synopsis from Anime News Network