Survival in Another World

It turns out that after he retired from the world, he just wanted to live an ordinary life, marry a wife and have a baby. When he arrived in another world, he just wanted to be an ordinary library administrator, marry a wife and have a baby. However, since a mysterious girl knocked on the door that night... Everything has changed. Is the legendary golden devil's contract true or false? Is there an alien apocalypse that can cancel the contract? What about the empire that disappeared five hundred years ago? Are the gods angry, or is there another hidden agenda? … Dual identities, dual careers, One light and one dark, the mystery is slowly solved! Everything is unexpected and everything is expected!