Attack on Titan (Japanese: 進撃の巨人 Hepburn: Shingeki no Kyojin, lit. "Advancing Giant") is a Japanese manga series written and illustrated by Hajime Isayama. The series began in Kodansha's Bessatsu Shōnen Magazine on September 9, 2009, and has been collected into 25 tankōbon volumes as of May 2018. It is set in a world where humanity lives in cities surrounded by enormous walls protecting the humans from gigantic humanoids that are referred to as titans. The titans vary in height and endlessly eat humans seemingly without reason. The story initially centers on Eren Yeager and his childhood friends Mikasa Ackerman and Armin Arlert, who join the military to fight the titans after their hometown is invaded and a titan eats Eren's mother, whom he swears to avenge on top of his determination to see them all killed. However, as the story progresses and the truths about the titans are slowly revealed to the reader, the narrative shifts to encompass Historia Reiss, squad leader Levi, Eren's father Grisha, and other supporting characters.