The story of Attack on Titan centers on a civilization inside three circular walls. According to the knowledge propagated locally, it is the last surviving vestige of human civilization. Its inhabitants, known as Eldians, have been led to believe that over one hundred years ago, humanity was driven to the brink of extinction after the emergence of humanoid giants called Titans, who attack and eat humans on sight. The last remnants of humanity retreated behind three concentric walls and enjoyed roughly a century of peace. Within the walls, the thought of venturing outside is strongly frowned upon and discouraged. To combat Titans, the country's military employs Vertical Maneuvering Equipment (VME), also called Omni-Directional Maneuvering Gear (ODM Gear): a set of waist-mounted grappling hooks and gas-powered propulsion enabling mobility in three dimensions. Swords made of ultrahard steel are used in conjunction with the gear, and eventually rocket launcher-like weapons called Thunder Spears are developed. There are different types of Titans. Pure Titans are the weakest and most generic, whose behavior is easy to predict, making them easy to kill. Abnormal Titans are Pure Titans whose behavior is more difficult to predict, making them far more dangerous. The Nine Titans, also known as Titan Shifters (Attack, Colossal, Armored, Female, Beast, Jaw, Cart, War Hammer, and Founding), are the strongest Titans; each is able to shift back and forth between human and Titan form to access their Titan's abilities.

You lives in the town of Shiganshina, located on the outermost of three circular walls which protect their inhabitants from Titans. In the year 845. You discovers a mysterious ability to turn himself into a sentient Attack Titan. Additionally, regaining memories of your father giving you this ability shortly after the fall of Wall Maria.

These events draw the attention of the Survey Corps and their commander, Erwin Smith and others, who intend to use your power to reclaim Wall.