MTL - Start From Soul Society and Cutting Through All the Worlds - Chapter 104 Everyone who comes out of Rukongai is ruthless.

Office worker Leon is reincarnated into a particularly punishing dating sim video game, where women reign supreme and only beautiful men have a seat at the table. But Leon has a secret weapon: he remembers everything from his past life, which includes a complete playthrough of the very game in which he is now trapped. Watch Leon spark a revolution to change this new world in order to fulfill his ultimate desire…of living a quiet, easy life in the countryside!

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.

If I were to fall into a game, I wish I would fall when I was young.

have you heard of it?

If you turn on the music player in the dead of night, put on headphones, hide your head in the quilt, and listen to the looped single repeatedly.

Fall asleep after looping forty-four times. If you are unlucky and open your eyes again, you will no longer be lying on your own bed, but will enter a strange space that is completely isolated from reality.

That space… On the surface, it looks like the places we usually see, such as our bedroom, living room at home, underground garage, bathroom, basketball court, construction site, etc. But if you look closely, you will find that it is different. …Everything is different.

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This is the experience of an ordinary person who, after acquiring superpowers, transforms and grows step by step in a blind corner, reaching the ultimate level.

- Description from novelbuddy