Attack on Titan (進撃の巨人 Shingeki no Kyojin, lit. "Advancing Giants") 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 15 tankōbon volumes as of March 17, 2015. It is set in a world where humanity lives inside cities surrounded by enormous walls as a defense against the Titans, gigantic humanoid creatures that eat humans seemingly without reason. The story initially centers on Eren Yeager, his adopted sister Mikasa Ackerman and childhood friend Armin Arlert, who joins the military to fight the Titans after their home town is invaded and Eren's mother is eaten. However, as the story progresses and the truths about the Titans are slowly revealed to the reader, the main narrative shifts to center more around Historia Reiss, one of the top soldiers from the Survey Corps.