MTL - The Crown Prince Chases His Wife - Chapter 149 where

She, a modern hidden ghost leader of an organization which gathered insane prodigies proficient in the various differing skill-sets. Highly skilled in medicine and poison, executes covert assassinations, viewed as insane and demonic in the eyes of people of the world. Killed in an accident, and reborn into the body of a disfigured young girl.

What? Face disfigured, identity stolen? A return to the family dim and hopeless? Her identity can be given up, her family can be forgone, but as for the one who harmed her predecessor who inhabited this same body, if she didn’t at least make them scream in unimaginable agony and throw them into a state of wretchedness, how could she live up to her demonic reputation? Endless turmoil ensues and it’s a battle to dominate over all! See how she shook the world dressed in a suit of red, her sword up against the dominant powers that rocked the Heavens! Her name spread across the seas, shocking the earth!

- Description from Novelupdates

William Scott, a soldier, returned to the city with the goal to live the rest of his life peacefully. He would practice the lifestyle of a retired person.

However, his mother set him up on blind dates time and again. Unwilling to keep up with her arrangements, he was left with no choice but to pretend to be in a relationship with Yvette Quinn, a female CEO who was also forced by her parents to go on blind dates.

To his surprise, this was only the beginning of many troubles to come. Before he could get to settling those troubles, he first needed to sort out an even more pressing problem.

The girl looked at him and asked, “Take a guess. Am I the elder cousin or the younger cousin? As my boyfriend, you should be able to differentiate between the two of us, right?”

His contract girlfriend was so unprofessional. Although they had an agreement, she was always asking her younger cousin to take her place and pretend to be her around him.

What should he do about that?

Masterpieces such as 'The Divine Comedy', 'The Theory of Evolution', 'Encyclopaedia Britannica', 'The Theory of Relativity'...Born in the history of human civilization, possess mysterious and magical powers in another world!Original sin, biological evolution, mastery of all arts...By reading the secret tomes, one can gain a variety of powers!The only trouble for the people of the other world is that they find it difficult to understand the texts from Earth.At this time, there comes a librarian from Earth...

I met the male lead in prison.