Heroines, Villainesses, and the Hero's Yandere Harem? I want them all! - Chapter 15: An Oversight

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.

A lonely soul, which was placed under the care of the Lord Protector’s Manor, ended up having her lover stolen by the family’s eldest daughter and dying tragically the day before her wedding.

Somehow, she was reborn in the family as their 14-year-old first wife’s daughter, Ning Xueyan, with a startlingly familiar face.

Step by step, she will ruthlessly scheme to seek revenge as well as uncover the mystery of her tragic death.

Her former fiancee, the flirty crown prince and the bloodthirsty prince, will now bear witness to a vengeful Ning Xueyan becoming the peerless lady of her generation…

- Description from Novelupdates

My name is Chen Mo, a gaming nerd.Recently, I've been obsessed with a single-player game called “Absolute Immortal” and have defeated the final boss, [Lady Yu], over a hundred times using cheats.Then, I transmigrated.I became Lady Yu's lackey.On my first day at work, why does it feel like Her Majesty is looking at me strangely...?...My name is Yu Youhan, Imperial Consort of the Yuan Dynasty, with immense cultivation power, dominating the nine provinces.I recently had a 'dream'.In the dream, I was wantonly tormented by a man, utterly powerless.I initially thought it was a mistake in my cultivation, thus giving rise to a heart demon, until that 'inner demon' appeared right in front of me......Within the high walls of the deep palace.'There are many ways to conquer a heart demon, it doesn't necessarily have to be through force...''Your Majesty, I, I admit defeat!''Who allowed you to admit defeat? Dare to defy this palace, and you'll be punished for another hour!''...'