Videogame: I Can Turn Waste Into Treasure - Chapter 79 - : Medicine Making

The world experienced a cataclysmic change, and countless spatial gateways appeared out of thin air.

A scientific genius named Thomas Harrier was transmigrated to an imperial prince body after a car accident that took his life. He found out that he is in a world similar to our own with a timeline akin to early twentieth century. The body that he is occupying was the imperial prince of a failing empire who suddenly rose to power after a successful assassination attempt of his father. Unaware that the attack is just the beginning of what is to come. He faces many challenges throughout. Will Thomas Harrier be able to live his second life in peace while running an empire and getting it back to its former glory? Or will he succumb into a conspiracy lurking within the country's borders?

Expect some:

Cold war era techs.

Super battleship with advanced electronics, propulsion, and fire control systems?
Helicopters?
Missiles?
Modern medicines and equipment?
AC-130?
A nuke?
Challenger or Abrams or Leopard?
F-4 Phantom or MIG-21?
Colored TV's.

Everything!!!

PS. Cover not mine, I just found it on google.

The story follows the protagonist, who wakes up one day to find himself in the body of Licht, a villain from a novel he was reading. Licht is a notorious villain who is known for his cruelty and ambition. However, the protagonist soon discovers that he has a natural talent for villainy. He quickly rises through the ranks of the evil organization and becomes a powerful force in the kingdom.

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.