Ichiban Ushiro no Daimaou - Volume 6, Chapter 3 — Literature is Difficult?

Enemy of the world, cursed by all, Kim Sungchul goes on a quest to prevent the ‘prophecy of the end’ from coming to pass.

But no matter how much he raised his strength, there were still some things he could not achieve with physical strength alone.

Resolving to obtain the power of magic, he goes into hiding to learn magic from his most hated of enemies, The Mages.

A skilled but unfortunate modern-day assassin was killed in a freak accident. However, he soon found himself summoned to another world by an evil wizard, who had him possess the body of a boy as an experiment. After successfully planning the evil wizard’s downfall, he used the wizard’s body as a springboard to gain influence and power in his new world.

- Description from Novelupdates

The eldest son of the assassin aristocrat Tuatha Dé.

The skill, experience, knowledge of the previous life, magic, all of which grows his power as an assassin.

Excellent assassins pass through. He was usually admired as the ideal lord, and behind it wielded a blade as an assassin aristocrat.

Past life, her spirit root was dug out from her body. She had wholeheartedly dedicated herself to the just path, but she was sentenced as an evil demonic cultivator.

Returning back to her juvenile years, she turns the tide. Against natural order, she had been reborn. Those who had deceived and humiliated her, she would return it to them a hundredfold with additional thanks.

Studying her own blood vessels, she recasts the best quality spirit roots. She destroys those rascal clansmen and returned home with glory!

The rules of the world do not hold her down; this time around she kills through the righteous path.

He is the universally admired spirit emperor, high above others, cold, proud and aloof. But every night he sneaks into her room and takes liberties. “Little runt, won’t you think it over?”

“Do I have a choice?”

“You can choose from giving birth once or giving birth twice.”

“Why must I?!”

“Because you stole my heart.”

- Description from Novelupdates