 The story of Attack on Titan revolves around the adventures of Eren Yeager , his foster sister , Mikasa Ackerman , and their childhood friend Armin Arlert . After the wall which protects their hometown of Shinganshina is breached by the Colossal Titan leading the other Titans to enter , Eren watches in horror as one of them eats his mother . Vowing to kill all the Titans , Eren enlists in the military , along with his friends . 
