Jitsu wa Ore, Saikyou deshita? ~ Tensei Chokugo wa Donzoko Sutāto, Demo Ban'nō Mahō de Gyakuten Jinsei o Jōshō-chū! - Chapter 22.2 - Dragon-sensei is Quiet (2)

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.

He is a young man without a spirit root. It is believed that this denies him the chance at cultivation. However, a mysterious lady imparts a Supreme Demon Classic to him and from then on, he starts his path of cultivation.
He undergoes a total transformation to emerge as the most fearsome and powerful fiendish demon in his era, that even immortals and fiends are fearful of him, and saints are at his beck and call.
Mastering the Supreme Demon Classic is the turning point in his life. He is able to unleash his immense and divine power from within, illuminating the entire universe!

- Description from Novelupdates

This story is centered around the man named Yi Ji-Hyuk, who has spent 1000 years in a Medieval Western fantasy-like world before returning back to the modern-day Earth. When he returns, he finds that his home is facing monster threats, and that humans with superpowers have appeared to protect the innocent people of Earth.

Read the first chapter. You will probably like it. ;)