Reincarnation: My Possessive Beast Husband - Chapter 76 - : Hoarse Voice

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 fallen ones, strange monsters that showed up on earth with the sole purpose of destroying everything and ruling over humans.Only one man remained during the onslaught, his name, was Rashin Montero.“Do you wish to live or die?”The question appeared before him.“Kill me assholes!”He died.A hundred years passed and Rashin finds himself alive in the future.It turned out he was saved by a stray angel, and was granted a powerful energy that allowed him to stand on equal footing with the monsters that once wanted to take over earth.In his new future, the world has been restored to what it ones was, a huge shield was placed around the world to keep the Hakiaas out.Heroes were summoned to defend the world against these monsters during the Countdown, while the monsters could not be killed or harmed, they could still be sent back to their world.Or at least, until Rashin arrived.[Blacksmith System activated. Welcome host.][Initializing core functions... Complete.][Congratulations, you have gained a new blue paint (Large sword.)][Stella blade has passed all requirements to evolve.][Evolving to human form can now be processed.][Congratulations, you have gained a unique core, your weapons can now undergo fusion.]Having a system that allowed him to craft weapons of all kind, Rashin enters this new world trying to survive while also remembering part of his memories.Not just that, he can also turn every weapon he makes into beautiful overpowered maidens capable of killing the Hakiaas aka fallen ones.

In the end of the era, the ghost wizard was killed in a car accident, the soul crossed, and he found himself in Japan, and he was attached to a Japanese.

I was thinking about taking a name in Japan, and I picked up a newspaper and glanced at it –

Kudo Shinichi, Sherlock Holmes of Japan’s Heisei, the savior of the police? In the trough, how does Laozi wear into the world of the second yuan? Well, all in all, this is a story of a wizard playing a passerby in the Conan world…

- Description from MTLNovel

In the 21st century, a young judge time-travels to another world.Here, martial arts are evergreen, and myriad schools compete for dominance.Confucianism: Immense righteousness, impervious to all laws.Legalism: The power of rules, the law follows the word.Military strategists: The power of conquest, invincible in battle.Mohism: Ingenious mechanics, ordinary humans rivaling gods.Yin-Yang school: Numerology and the five elements, seeking divination, pursuing good fortune, and avoiding disaster....What's this? The Legalists grow stronger by adjudicating cases?Li Nuo, who has just vowed to advocate for the people and eliminate the corrupt, discovers that his father is the greatest villain in the court.Faced with countless enemies seeking revenge against his father, Li Nuo says he only needs one sentence.'My lady, guard me!'