A serial killer with a guilty conscience is a strange choice for someone to be reincarnated into another world. However, the Goddess that greets death row prisoner 567 after he dies has a history of poor decision-making. The 12 heroes she had selected to slay the Demon King went on to become greater monsters than the evil they defeated. In the Goddess' mind, it only makes sense that these reincarnated heroes must be killed by another person who is not of this world.

Although coaxing at first, the Goddess eventually reveals that the serial killer has no choice but to comply with her demand. The reborn killer—now named Shirukyi—must carry on murdering, regardless of any personal feelings. While the Goddess previously granted her champions special "cheat" abilities, Shirukyi is solely given knowledge about how the former heroes operate. Combined with this information and a killer's skills, Shirukyi's intrinsic understanding of human depravity will be the means to success.