Infinite Mana In The Apocalypse - Chapter -1 - Ranks/Levels/Realms(Spoilers as of 317)

The definition of a villain according to Kim Sangmin: The person who has to die for the story to end.But his story had just begun when the villain of the book he was reading died in the end, and he woke up to start the story again.As he uncovers the hidden, untold truths behind the cascade of a villain, the more he leans towards becoming a true villain—only in pretend, of course! He has a little brother to take care of, he can't just die and leave him alone. He's also his baby brother's role model, so he has to teach him how to live a long life by becoming a hero instead!And how does he plan to become a hero?Obviously, by stalking the actual main character of the book and overtaking his spotlight at every chance. Step by step, he would overthrow the 'real' hero of the book and change his status to one with praise.Easy, right?

I exist in the darkness, disappear under the bright light, and will eventually devour the sun and turn into the shadow of all things… Known by people as the indescribable terror of darkness; the king of shadows; the dark day; the existence of the shadow of the world , is still just a somewhat special high school student, facing a weird death game…

- Description from novelbuddy

This book is about baby-making.

What the heck? She, a famous doctor from the 23rd century, turned into a village peasant girl of a different world!