Rakuin no Monshou - Volume 6, Chapter 3: The Sorcerer Garda

He was straight.Even after dying and waking up as the protagonist in his sister’s BL web novel.He was straight.Even with all the male leads practically throwing themselves at his feet.He was straight.Even when his heart inexplicably skipped a beat during romantic moments with one of them.He was straight.Even now... when he could somehow get pregnant.He was straight.There was no denying it.HE. WAS. STRAIGHT!“So, can someone please help me get out of this goddamn novel already?!”[Warning: 18+ content and there will be some themes of non-consent, mentions of abuse and suicide.]

The grand master of Shape-Will Fist, Ning Wufeng, was brought to the Divine Land Continent by a mysterious scroll. In this world, he was an abandoned child and appointed by his family as inferior leader of a small fishing village because he was unable to open up his Spirits Aperture and begin his cultivation.

However, he seemed destined to open up his abandoned with the memories of previous life integrating into his mind. And the scroll guided Ning Wufeng into a vast mysterious hidden world where he was bestowed divine weapons and acquired supreme skills of cultivation.

Deafening thunder indicated the immense changes in the movement of winds and clouds. In a world where people worshiped martial arts, how could the teenage loser be the master of his own destiny? How could he wield his power to control the world, making gods and demons tremble with fear?

- 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.

After a sudden and inexplicable transmigration, Maximus finds himself in a fantasy world where extraordinary power exists. But he is not without his advantages; he possesses a system that grants him the ability to become stronger as he takes on wives and birthed children.Determined to conquer this new world, Maximus uses his cheat to gather wives and birth children, building up his power and influence. As he gains more allies and resources, he sets his sights on the ultimate prize: ruling the world and surpassing even gods.However, the road to conquest is not an easy one. He must contend with powerful factions, rival conquerors, and unexpected challenges as he builds his ideal empire. But with his cunning mind, he is determined to succeed and become the greatest conqueror the world has ever seen.