Chen Rui, an otaku from earth, is reborn in a human body in another world, falling into the legendary, evil, brutal Demon Realm, inhabited by Devils called Mozu and where humans are treated as food. He has to survive while facing horrifying devils, poison dragons, and a variety of powerful enemies by using on a strange Super System chip and his wits, surrounded by the Devil’s beauties such as the black-bellied lolita princess, the iceberg queen, the violent scythe, and the charming succubus. 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 his power and strategy step by step starting from an ordinary human to writing the legend as the devil’s greatest son-in-law.