Citadel for All: The Only Unit Angel at the Start of the Game - Chapter 508

Branded a scammer, a thief and a con artist, Si-eun became a fugitive following the betrayal of his friend and sworn brother Javier, the one who stole his life's work, his business from him and framed him for its downfall. Hunted by loansharks and enraged investors for months, he wandered from city to city until his luck eventually ran out.At the moment of his pathetic death, a god intrigued by his desperation to live offered him another chance at life—Only for Si-eun to awaken inside a familiar world, the world of an MMORPG game he once played, even worse… he inhabited the body of Azazel Von Astavore, a useless extra destined to die in every playthrough of the game.

The celestial celestial beings who lived for more than 100,000 years were born and reborn in a small monk in a human world.
His motto: “It’s not as good as a medicinal medicine for ten years of hard work.” “Even if you practice a copper-iron bone, it’s not enough for my soldier’s attack.”

- Description from Novelupdates

Our protagonist Caam is a man from Earth that was reincarnated into this world as a demon. In order to survive, he spared no effort in avoiding the sparks of battle and without noticing it, he became strong himself.