Kuro no Senki: Isekai Teni Shita Boku ga Saikyou na no wa Bed no Ue dake no You desu - Vol. 2 Ch. 5.1

[MangaDex]

 

[FlyingThunder]

why do so many isekais have such a weird "i have genius knowledge of my world and kickstart industry for new products in this medieval world" fetish?

 

[DanYHKim]

"Here comes the plane."

Uh. "Plane?"

By the way, before airplanes, the thing we call paper airplanes existed, and were called "paper darts".

 

[DanYHKim]

why do so many isekais have such a weird "i have genius knowledge of my world and kickstart industry for new products in this medieval world" fetish?

Because modern people from developed countries do know a lot. In the premodern period, people knew little else than what their immediate family knew. That often meant knowing how to farm and many home handicrafts. It was a wealth of knowledge, but of narrow scope.

A high school graduate, especially from Japan would know pretty advanced mathematics (i.e. algebra and geometry. Maybe even calculus, which wasn't invented until modern times). He also went on regular field trips that took him to different places and also included tours of different industries. He saw how paper is made, and may have learned some of the background history of papermaking in preparation for the trip. He may have learned how a locomotive worked, from modern electric ones to diesel, and maybe even steam-powered engines. He would know germ theory and how to control infectious disease through hygiene, public education, and infrastructure. A single TV show by NHK would have shown him the cycle of a year of rice cultivation with catfish co-cultivation for protein and fertilization. Another show might have taught him some aspects of forestry management, including coppicing and also cultivation of mushrooms. A third show or a book might have taught him basics of celestial navigation, the idea of the magnetic compass, and perhaps the potential of the chronometer to calculate longitude. Such a package of knowledge would revolutionize shipping, exploration, and naval warfare. Understanding vitamins, especially regarding scurvy, would be of immense strategic value. Being able to keep ships at sea for months at a time with the crew's health preserved can let a country blockade another's vital sea routes until they run out of strategic materials.

And that is just a high school education, two books, and three TV shows.