Miss Shen is Actually A Bigshot in Witchcraft - Chapter 40

A skilled but unfortunate modern-day assassin was killed in a freak accident. However, he soon found himself summoned to another world by an evil wizard, who had him possess the body of a boy as an experiment. After successfully planning the evil wizard’s downfall, he used the wizard’s body as a springboard to gain influence and power in his new world.

- Description from Novelupdates

“Seven years later, she returned with her baby

”Give me the child, and you can name a price!“

”Spring only sows the seeds. When it comes to autumn, you want to obtain a son. Heh, man, aren't you thinking too simply!“

”If you want me to call you daddy, then you have to show your ability to chase after my mommy. The man that my mommy likes is my daddy! “Otherwise, there's no need to talk about it!”

An Individual from Earth finds themselves in the Shinobi World, equipped with a Scientific System. From that moment, he delved into scientific research far ahead of its time.