The God Virus - Volume 2 - 23 ORIGIN

A man is reborn into the world of Avatar: The Last Air Bender as a waterbender from Katara's tribe. Best of all, he was the same age as her, and he had a system with him to help.He knows the future and a system that lets him continuously get stronger by completing quests or long-term missions, as well as giving him the ability to copy abilities from others for himself. He will become invincible in the world of Avatar, even more so than the Avatar himself.

The world that nurtured the civilization which reached the pinnacle of magic was on the verge of destruction.
The last survivor transmigrated to the past, when the magic civilization started growing, as countless mages were still fumbling their ways through the thorny paths of magic knowledge.
He, who came from the end of the magic era, aim to reach the pinnacle of magic.

- Description from Novelupdates

Xia Mi found himself transported into a classic JRPG game, becoming a villager in a beginner's village.His biggest wish was to save money and marry a woman from a different race as his wife, live a peaceful and worry-free life, and eventually pass away peacefully.One day, the heroes defeated the Demon King.[Name: Xia Mi][Profession: Villager]New addition: [Profession: Successor to the Demon King]“Quickly take action, Demon King! Kill all the heroes! Restore the glory of the demon race!”Wait, did something go wrong here?In the beginner's village, where Xia Mi spent his days farming and serving as a passer-by, he suddenly had an identity panel.But he was just a villager in the beginner's village!“Where is the Demon King? Where is the Demon King?”News of the Demon King's emergence spread across the continent, and every hero who came here to defeat the Demon King could see a constant stream of monsters in the beginner's village, but never caught sight of the Demon King.A villager from the beginner's village: Demon King? I'm just a villager. I have no idea what it is.