Interstellar Age - Chapter 352 A Dreadful Feeling

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.

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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

Nagasawa crossed to Naruto Universe and was bound to Konohagakure.If Konoha is severely damaged and destroyed, Nagasawa’s lifespan will be reduced.He panicked at the thought of the upcoming Nine-Tailed Demon Fox's attack , and the thought of Konoha getting destroyed left him in despair.Fortunately, while bound to Konoha, he can obtain templates of powerful characters.At the beginning, He got the Whitebeard template! Since it's the Whitebeard from the Summit War of Marineford, he can use Tremor-Tremor Fruit's ability and Haki.Facing the Tailed Beast Ball, which terrorized Konoha Shinobi, Nagasawa leaped and shattered the Tailed Beast Ball with one punch!

Another entry in what you can call the Proto Harem Series: the books written before the Harem Series that take place in the same world.

It’s about a swordswoman whose student is captured, so she goes to rescue her.