Akuyaku Reijou ni Nanka Narimasen. Watashi wa『Futsuu』no Koushaku Reijou desu! - Chapter 22: Mofumofu fever.

Su Ran, a music prodigy, woke up transmigrated into a book.

At that point in time, the main story arc in the book had already been completed. As a villainess female supporting character, not only did she need to take over the original owner’s pitiful life in poverty, she also gained an instant son right at his rebellious period.

Ten or so more years from then, the son would turn into a twisted, evil villain. He would appear in one of the extra chapters to pick on the male and female lead’s children.

***

Su Ran: Son, you shouldn’t be too outstanding.
Su Han: Why not?
Su Ran: ’cause you will be killed.

Su Ran: Son, would you like to learn music from me and become a zen, little fairy boy who only needs to drink dew.
Su Han: No, I want to go into business so I can support you.

- Description from Novelupdates

She thought she was going to be with a warm boy, but she didn't expect that she slept with an arrogant CEO accidently.

As soon as she entered the university and became a college student, she unexpectedly became an unmarried mother, even a twin. For the sake of children, she has grown from a simple little girl to a strong and independent single mother. Later, she found the children's father. In their long time together, they gradually fell in love with each other ...

Hakuto's life changes forever when his father Shin— a man with highly questionable morals—marries Kagura Kurotsuki, the CEO of a multinational company, and they move into her luxurious mansion.There, he meets the alluring daughters of his new stepmother: the seductive Yuzu—who doesn't hesitate to tease both her new stepbrother and her stepfather in ways that are... rather bold—and Rika, more introverted and irritable, yet just as sensual.But nothing is truly as it seems...Kagura is a succubus, but Rika and Yuzu are different.They were born from a demon and a vampire—something that shouldn’t be exsiste.Because of that, demons, vampires, even humans want them.But Hakuto won’t allow it.He’ll never let anyone hurt his beloved stepsisters.