From Soldier to Officer: A Game Addict’s Journey - Chapter 365 - : Professional Offense

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.

On the will left behind by the 14 year old suicide victim K:

“Taku Sugawara is the devil. Nobody should believe his words.”

Lee Jin Woo once lived a dismal life.
He lived pitifully on a day to day basis in his five-pyeon studio filled with mold.

Then, one day, he died in a sudden fire.

When he wakes up, he finds himself inside a novel.
But there’s just one issue…
He had become the novel’s villain!

Strong? Handsome? Savage? Badass?It's all about the intelligence quotient, my friend.————PS: Mutation shouldn't be mistaken for enlightenment.