Attack on Titan Before the Fall Vol 1

Attack on Titan Before the Fall Vol 1 by Ryo Suzukaze. An Action manga rated Teen, published in English by Kodansha in 2013.

Set decades before Attack on Titan, this prequel follows Kuklo, a boy born from the remains of a Titan's victim and shunned as a monster, as he struggles to find his place behind the Walls and fight back against the Titans.