### Instruction:
What is Attack on Titan?

### Input:
Attack on Titan (Japanese: 進撃の巨人, Hepburn: Shingeki no Kyojin, lit. 'The Advancing Giant') is a Japanese manga series written and illustrated by Hajime Isayama. It is set in a world where humanity is forced to live in cities surrounded by three enormous walls that protect them from gigantic man-eating humanoids referred to as Titans; the story follows Eren Yeager, who vows to exterminate the Titans after they bring about the destruction of his hometown and the death of his mother. It was serialized in Kodansha's monthly magazine Bessatsu Shōnen Magazine from September 2009 to April 2021, with its chapters collected in 34 tankōbon volumes.

### Response:
Attack on Titan is a manga and anime written by Hajime Isayama. The story follows a protagonist Eren Yeager who lives with his friends Armin and Mikasa within the three walls of humanity. Outside of these walls exist ferocious beings called Titans that eat humans. Eren watches his mother get consumed by Titans and vows revenge which kicks off the main story. The story has deep messages about war and genocide, and takes many unexpected turns.