Shingeki no Kyojin:

The story revolves around Eren Jaeger and his friends Armin Arlert and Mikasa Ackerman. In this world, the human population lives in cities surrounded by huge walls to protect the appearance of gigantic creatures that devour people : Titans . One day the Shiganshina district , located on the outside of the first wall called Mary , is attacked by a giant Titan causing a gap and opening the way for the rest of the Titans achieving invade the city , incident in which the mother of Eren It is devoured by a titan . After the chaos caused , and once they are safe , young people decide to join the army and fight the Titans themselves.