Chen Rui, an otaku from earth, is reborn into a human body in another world, who falls into the legendary evil, brutal world of the devil called Mozu where humans are treated as food. He has to survive while facing horrors of the devil, violent dragons and a variety of power enemies depending on a strange super system chip and his wits. Surrounded by Devil's beauties such as black-bellied lolita princess, cold queens, violent dragons, charming poisonous devils … Wanting to live in the Devil's world is hard! Wanting to live in the Devil's world as a human is harder! Wanting a human to be the devil's son-in-law is hardest! Let us see how a small otaku uses power and strategy step by step starting from an ordinary human to writing a legend as the devil's greatest son-in-law.