Kyoukai Senjou no Horizon - Volume 1B, Chapter 34: Those Running Toward the Borderline

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

"There is a thin line between poison and medicine, and I shall make you dance on it!"

Death is only the beginning….He is the boss of a small bar. Despite his gentle and amicable appearance, he is actually cold and detached. He was born with the ability to communicate with spirits but sealed it away, unwilling to get involved with the supernatural.She is a rather unqualified lawyer. Timid as a mouse yet hates evil with a passion. Her birthdate is inauspicious but she’s also blessed by Buddha.A weird and bloody case forced them together. Her cases grew more and more dangerous while his sealed abilities awakened and grew stronger. They were initially repulsed by each other, which turned to understanding, getting along, cooperating, and finally a mysterious yet fierce attraction. With the help of a friend, the two of them solve the city’s horror stories one after the other.