Overlord (LN) - Chapter 4

On the will left behind by the 14 year old suicide victim K:

“Taku Sugawara is the devil. Nobody should believe his words.”

A story in which a woman, after learning that the world would end in ten days, sets out to finish one last thing: murder her ex-girlfriend.

However, she ends up befriending, and spending the world’s final days with, the little sister of her ex-girlfriend instead.

While the demons were rising, mankind was about to become extinct. Six temples rose and protected the last territory of mankind.

A young boy joins the temple as a knight to save his mother. During his journey full of miracles and tricks in the world where temples and demons are antagonistic to each other, will he be able to ascend to the strongest knight and inherit the sealed divine throne?

- Description from novelupdates

Drugged one night by her ex-boyfriend, a mysterious man took advantage of her in an ecstatic night filled with sex.To take her revenge, she married the man, and used him.