Attack On Titan

A brief description of the Attack On Titan manga:
The plot of Attack on Titan revolves around the young Elen hunter, his adoptive sister Mikasa and his best friend Armin Arlert, who live together with the rest of humanity in cities protected by huge walls from the attacks of the so-called Titans, gigantic humanoid beings who seemingly devour humans for no reason. The walls that promised peace have existed for 107 years.