Attack on Titan

Year 845. For a century, the world has been ravaged by man-eating titans.
Humanity must live behind three gigantic walls to protect itself from the Titans.
Eren Jäger is 10 years old and lives with his parents and his adopted sister, Mikasa Ackerman, in the town of Shiganshina, located near Maria. The Maria Wall is the outer wall, the middle one is the Pink Wall and the middle one is the Sina Wall.
Eren dreams of joining the Exploration Battalion to explore the outside world. The fight against the Titans is led by an army divided into three branches: the Exploration Battalion, the garrison that protects the walls, and the special brigades that keep the peace inside the walls. While the humans have not seen Titans for more than a century, the city is attacked by a 60-meter Titan that destroys the Maria Wall.
Eren and Mikasa see their mother being eaten before their eyes by a Titan.

Eren decides to take his revenge and kill all the Titans by joining the Exploration Squad, the elite section of humanity's soldiers.