Toaru Majutsu no Index SS - Volume 1, Chapter 4: A Drunk Mother’s Circumstances. The_Two_Leading_Roles.

As a true over-bearing president scum gong, when Xie He for the Nth time rejected his admirer, he heard a sentence in his head: “Congratulations on achieving the “rejects 100 hosts” accomplishment; as an award you will soon bind to the “Scum Gong and Cheap Shou” system, entering other worlds to complete capture missions.

As a scum gong, Xie He expresses that it is very easy to hide one’s true colors, but…“I Heard My Boyfriend’s Brother Secretly Loves Me,” “Teacher Love Me One More Time,” “Raising Youth Manual,” “Your Majesty, This Servant Obeys,” “The Tyrant Lord’s Substitute Lover,” “Captive of the Empire,” “Disciple’s Cultivation Furnace”…

Xie He: Wait a minute. These words sound really strange… and why is my role the ‘cheap shou’?

System: Fighting poison with poison. Using scum to overcome scum. I’ll be relying on you to abuse the scum gong! Remember to not OOC~

Xie He: He he.

Later…

Xie He: Hm? You say all the scum gong love me? Sorry, I only love myself.

- Description from Novelupdates

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.

This is a world where humans, demons and mysterious beasts coexist. Humans cultivate mysterious qi. Demons cultivate corporeal bodies. Mysterious beasts cultivate soul perception. A legend says that in the middle of an endless rainforest, there are extremely powerful existences; they are called demon kings. Some demon kings have a tyrannical corporeal body, some are experts in illusions. Some demon kings are proficient in magic, some can even move mountains. Some demon kings are able to sense things thousands of miles away. These demon kings rarely appear in the human world. Even if they emerge in the human world, they would reincarnate in human form; assimilating with mankind while seeking to breakthrough realms…….

After his fall, the Duke who was distant with his wife and daughter recalled his memories of another world. With a new perspective on life, he swore to cherish and protect those two.