Defiant Martial God - Chapter 120: The Demonic Blade Rebels

Some say reincarnation is a blessing, but for me, it's a dreadful curse. Cursed with endless reincarnation, I've been reborn as a villain 137 times. And all 137 times, I've been toyed with and killed by heroes who are far more cruel than the said villains... If I can't win no matter what I do, then I'll crush those so-called heroes at their very roots. - Quality Fan Translations, Made by Fans for the Fans - Villain Takes Over The Academy

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

Shen Yinning was originally the Crown Prince Lu Ying's childhood sweetheart and fiancée, but due to her father and brother's rebellion, she was exiled to Gan State and married to a minor local official as the daughter of a criminal. Meanwhile, Lu Ying gloriously married her cousin Shen Yunxi as his Crown Princess Consort.Three years later, Shen Yinning returned to the Capital with her husband. Everyone praised the Crown Prince and Princess for their mutual respect and harmony, and Shen Yunxi often flaunted in front of her how loving she and the Crown Prince were. However, only Shen Yinning knew that the seemingly restrained and honorable Lu Ying came to her chamber every night, completely disregarding the fact that she was now someone else's wife, secretly claiming her and keeping her as his Forbidden Fruit...

A 34-year-old NEET otaku, chased out from his house by his family, found that his life is reaching a dead end. He then recalled that his life could actually have been much better if he had made better choices in the past.