Rank F Demon King

They summoned me to be the Demon King. Not just any Demon King — the legendary one, the one from the prophecies, the one who levels kingdoms. Small problem: I'm Adrian, I'm in my twenties, and five minutes ago I was heating instant noodles in my kitchen. The big problem is what the System says: Class: Demon King (Legendary). Rank: F. Turns out a title isn't power. Three broke adventurers dragged me out of my world with a ritual that went wrong, and now a pact sinks or saves all four of us together. To get home, I have to take my class to max rank. To rank up, I have to complete quests. And to complete quests, I have to start at the very bottom: exterminating rats, escorting carts, and convincing half the world I'm not the apocalypse the Church of Light has waited a thousand years for. Which would be easier if the beasts didn't kneel as I walk by. And if the kingdom hadn't just put a price on my head. One quest per chapter. From Rank F, up. What could possibly go wrong? — Description from novelcodex.org