Singer Sailor Merchant Mage - Chapter 80: Yoga Yoda Yogi

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.

Birth rates are decreasing. Hope is vanishing. The world has gone gray.Humanity, drifting in quiet collapse, receives an email.Every person on Earth. Simultaneously.The Aegis Mandate.Disguised as a cosmic aptitude test, it triggers The Incident of Separation—a global psychic cataclysm that erases identities, wipes memories, and divides all survivors into three factions: Law, Neutral, and Chaos. Overnight, cities become battlegrounds. Apartments become dungeons. Ordinary people become monsters—or the ones who hunt them.Ragnar Vhagar was just a loner university student. Now, thanks to a system he didn’t ask for, he’s a newly minted Demon King, locked in a crumbling apartment with goblins under his sofa and a glowing soul crystal next to his frozen peas. His new job? Build a deadly domain, defend it from invading “Heroes,” and somehow level up fast enough to not die.Alongside him is Isabelle Thorne, a razor-sharp warrior of few words and one very sharp sword. Their reluctant alliance, born in blood and snark, evolves into trust—and maybe something dangerously close to affection—as they rise together through the layers of the game-like world they’re trapped in.With each conquered domain and defeated boss, Ragnar realizes the truth: the dungeons aren’t meant to crown a winner. They’re meant to break the players. The Law faction wants control. The Chaos faction craves destruction. But Ragnar? He wants something they’re all too afraid to say out loud:Freedom.In the ruins of Kanta’s ogre stronghold, Ragnar and his misfit warband take their biggest step yet—claiming a kingdom, unifying a fractured system, and preparing for what comes next. The Heroes are watching. The gods are stirring. The world is watching a war.And somewhere deep beneath it all... Ragnar is rewriting the rules.

Intellectual Villages are old fashioned rural villages recreated with cutting edge technology. Those villages attract the Japanese monsters known as Youkai.

The high school boy Jinnai Shinobu lives in one of those villages and has a Zashiki Warashi living in his house. He tends to run across Youkai with unnerving frequency and this often leads to trouble for him.