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.