Brothel Manager : Unexpected Encounter with A Hidden Family Heirloom - Chapter 9 - : Melons & Mountain peaks

If you had a chance to live again, what would you do? Earn money, hold onto a thick leg, just find someone to live a happy life with? Ha ha… Stepping on the beat of the times, riding the wind and breaking the waves, strategizing, using your knowledge to change yourself, and everything around you, come back! The reality flows to the plot, the golden fingers are thick, slow, and cool.

- Description from Novelupdates

The top-tier professional player Lis woke up to find himself having crossed into the “Divine Revelation” game, becoming a Viscount enamored with magic. Knowing that he would soon face a continent engulfed in war smoke, grand otherworld expeditions, the mysterious decay of the World Tree, and the constant threat of Abyss Demon invasions... Lis admitted he was a bit panicked. ...... Fortunately, the game system was still in place, and he still possessed the “All-Purpose” Talent. With the memories of his past life, he switched his class to Arcanist, analyzed the Element Model, reshaped the world’s rules, and step by step ascended to that supreme throne. ...... Players complained about him, “This boss is too perverted, he can even grow stronger, we protest!” Elves worshiped him, “Lord Lis is the strongest Divine Favored, he has brought peace to the world.” Mages praised him, “He is the pioneer of magic, as well as the Guardian. His revered name is Lis Kane, He is the god of the arcane.”

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.

A military enthusiast with dreams of serving, shaped by his father’s influence and a bookshelf full of war theories, finds himself unexpectedly reborn into a fantasy world he’d recently read about.Now an orphan, he faces impending destitution in a land governed by strict caste systems. But with the Reich Empire Academy Entrance Exam as his potential salvation, he’s armed not with magic, but with a vast knowledge of military tactics from his past life. As the date of his expulsion from the orphanage looms, he’s determined to leverage his unique skills to change his fate.