Danmachi: Clones System - Chapter 16 - Creator’s Mask.

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.

Never touched a girl for five years, living in isolation, and having no skills or idea to talk to a girl.

Tim never thought he would reincarnate in the game he was working on. Now, he had to go through a life that almost seemed impossible for him.

With the Lust System that he created, Tim was forced into a Murim World where strength was everything. And, the only way he could level up was by getting a new girl by his side.

The skills that he could only buy from real currency can only be accessed through quests now.

Can he survive in this world? Can he live with this new life where he has to touch a woman every day of his life? Can he reach the top of the world with his harem?

Awakening to a post-apocalyptic world infested with zombies and mutated monsters, Alex makes a startling discovery: he possesses a system that grants him access to unlimited resources every day.【Congratulations, you've received unlimited bottled water.】【Congratulations, you've received unlimited 9mm bullets.】【Congratulations, you've received unlimited cold medicine.】...With each system notification, Alex's chances of survival soar while others struggle to stay alive.As everyone else fights for their lives, Alex finds himself living in luxury, residing in a lavish mansion where he leisurely sips red wine and savors grilled delicacies amidst the chaos of the end times...

In a future timeline, the earth was visited by a species known as the Slarkovs.
Having lost their home planet and in search of a new one, earth was the next habitable planet for them.

Humans and Slarkovs made a deal with each other in return for the Slarkovs living on earth.
The Slarkovs traded their technology and knowledge for a new home.
They were similar to humans except for some of them who had slight differences so fitting into the society wasn't a problem.
Over the years Slarkovs and humans began to mate with one another and reproduce offsprings.
This in turn created a new species known as the mixed-blood.
Centuries later mixedbloods could tap into their bloodline and perform unimaginable feats.

Gustav born into an age where bloodline determines everything, struggles to fit with a useless bloodline.
His bloodline only grants him the ability to change his hair color, destroying his hopes and dreams for a great future.
His fate is turned around when an unexpected situation leads to him finding a system that grants him the power to unlock and upgrade bloodlines by completing quests but he's baffled by two quests with a five-year deadline. Success will grant him unimaginable rewards...
But only one thing awaits him if he fails... Death!

Follow Gustav on his interesting journey filled with unprecedented adventures, danger and death, maybe?