I Leveled up from Being a Parasite, But I May Have Grown Too Much - Chapter 61 - Eiji Choukai

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.

Where does the game end? Where does reality start?

When one very anticipated VRMMORPG was about to be launched, and Jake was one of the first players to have a chance to access it, he had a weird dream of himself fighting massive beasts and then seeing a world being destroyed.

Without knowing any better, Jake assumes that it was just a weird dream, but then he begins to have those weird dreams again and again until they become even more vivid, and much to his surprise, whenever the dream changes, he obtains a new power inside the game.

It doesn't take long for Jake to realize that he isn't the only one who has those dreams, and soon enough, Jake realizes that the game and reality are a lot more connected than he thought.

21st century kid got onto a virtual game 600 years into the future, with a freak combination of events gets to play as a NPC!

The first system job is to undertake the roles of helping new players create their character. Want to choose as one of the hidden race? OK, this is a slavery contract, up to you to sign it or not!

Entering the game as a player and creating a personal game character, the only advantage I have… The choice of selecting a powerful race!

Walking alone to the peak, bringing the present world to advance by leaps and bounds, the abnormal path starts from this first step!

- Description from Novelupdates

Nagi who was summoned to another world acquired the「Skill Structure」skill.

Nagi felt the hints of black job from the king’s request 「To defeat the devil king」. He leaves the castle and starts his journey with a slave girl.

The small demon girl Cecyl, the melee-fighter beast girl Rita , Aine the onee-chan maid, Regii the cursed sword.

Rafiria the warm and fluffy elf and Iris the sea dragon shrine maiden.

Nagi rewrites the girls’ skills and made them into 「cheat characters」one after another.