Michin Hwangjega Doeeobeoryeotda

Park Gwang-Seok is an average office worker who enjoys reading web novels as a hobby. And as he's reading one night, the author of his favorite story, "The Great Demon War," asks him to save the world. After a flash of light, he finds himself sitting on a throne in the body of Emperor Axeltrion, the villain of the novel. But the worst part is that Axeltrion's murderous instinct makes him crave bloodshed! Can Gwang-Seok save the world and fight the urge to kill anyone who even slightly annoys him?

(Source: Tapas, edited)