Killing Killer

The main character, Siwoo Lee, lost his parents to a murderer 10 years ago. Finally, he meets Jack, the killer who killed his parents, and beheads him
. “It wasn’t me who killed your parents.”
After learning that the real culprit is a ‘contractor’ belonging to a group of killers using superpowers, Si-woo Lee decides to hunt down the registrants with Jack’s help.