Juujika no Rokunin

Juujika no Rokunin summary:
”Is it okay to kill people?"
A treacherous revenge suspense by Shiryu Nakatake, a newcomer to Bessatsu Shonen Magazine.
"Shun, if someone is converted, let him go and do nothing. He should be given a chance to be reborn."
"Grandpa, I hope he doesn't reincarnate himself."
In order to defeat several non-human monsters, the boy also became something non-human.
Shin Uruma, a sixth-grade student, was named "Experimental body: A" by five of his classmates and was severely bullied and lived in hell. His only peace was with his brother, who loved him, and his parents, who protected him.... . until the five monsters killed his family.
When he finally loses everything and faces true hell, a dark "wish" is born inside Shun. He was reborn under the training of his grandfather, who served in a secret unit during WWII. Now, four years later, he appears in front of his fated enemy.
"I won't let ANYONE get in the way of my revenge."