The New Hire is the Demon Lord

Dullahan, the demon lord who once terrorized the world, finally revives in modern-day Korea, eager to take revenge against the hero who defeated her centuries ago. But all she can find is his descendant, Yongrae Kim: a hapless, incompetent office worker with no prospects and no joy in life. Ending his life now would only be doing him a favor, so Dullahan decides to improve his life first… but Yongrae's two-timing girlfriend and his many strict superiors at work stand in the way. Can Dullahan crush the office hierarchy and awaken Yongrae's dormant hero abilities to make her revenge more satisfying?