Juujika no Rokunin

Labeled "Experiment A" by five of his classmates and tortured throughout sixth grade, Shun Uruma hung on by a thread. When his bullies targeted his family, leaving him with nobody but his grandfather, it was the final straw—Uruma had suffered enough. Determined to get back at his enemies, Uruma begged his grandfather, a WWII veteran, to guide him through the path of vengeance. Four years later, Uruma completes his intense training and embarks on a brutal journey of torture and retribution to hunt down the five monsters who made his school life a living hell. [Written by MAL Rewrite]