MTL - Sugar Baby - Chapter 53

A skilled but unfortunate modern-day assassin was killed in a freak accident. However, he soon found himself summoned to another world by an evil wizard, who had him possess the body of a boy as an experiment. After successfully planning the evil wizard’s downfall, he used the wizard’s body as a springboard to gain influence and power in his new world.

- Description from Novelupdates

Hu Feng, a high school student, accidentally embarked on the road of modifying the world.

Forty years ago, demons invaded the eastern continent. Coming from another realm, they hunted the humans, and people soon began to wage war with them. Before long, there were those among the humans who inherited the demons' abilities.Demon hunters are currently the most in-demand profession. Although the chance of dying during a raid was high, the hunters were mostly popular among the common people. If you have some demon blood in your body, then the path to the Hunter's Association is open to you.Year 2066, Seoul. The territory of the former city is divided into three parts. Green Zone, Orange Zone and Red Dangerous Zone. Although mostly ordinary people and workers lived in the green zone, there was a chance for demons to get into it. That's why demon hunters patrol the whole area, sacrificing themselves for the lives of people.The main character, Lee Ki-hyun, inherited 50% demon blood and became the world's first SSS-ranked demon hunter. He will have to go through the path of a demon and learn the truth about his parents to save humanity.