Demon King: I Just Want to Retire

My name is Lucifer Shadow Lord, the Demon King of the Abyss. I have destroyed the world, torn apart gods with my hands, and ruled the dark world for a whole thousand years. But now, I just want to retire. Tired of the 996-style management of the demon world, and fed up with the challenge of brave men checking in every year, I faked a gorgeous death, locked up 99% of my power, pretended to be a powerless young man, sneaked into the most powerful university in mankind under the pseudonym "Xifa", and applied to be a librarian. Food and accommodation are included, and the monthly salary is three gold coins. The daily work is cleaning and borrowing books and registering. There's sunshine, there's a rocking chair, and most importantly - no one knows me. This is where my retirement life begins.