Re:Zero Kara Hajimeru Isekai Seikatsu - Volume 4, Chapter 58 [Grandma]

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 boy wakes up with omnitrix as a X-GENE

Drunk, I lie on the lap of a beauty; awake, I command the power of the world.From being unknown to dominating the world, when Lin Fan looks back on the path he has traveled, it is all laid out by beautiful women!

Many islands dotted the vast oceans of this world. However, some of the islands were a lot more sinister than the rest. Those islands, known as Nightmare Islands, were true nightmares to all but the strongest and most fortunate. Children were kidnapped and thrown on these isolated islands by the Nightmare Palace, forced to sign soul pacts with evil soul pets: Nightmares. These devils slowly devoured the souls of their trainers to grow stronger. If the children did not cultivate fast enough, their souls will be devoured whole, leaving only an empty husk behind.

Chu Mu, the protagonist, was an heir to the Chu Clan, but due to a plotted murder, he was thrown on the island, sentencing him to almost certain death. Dancing on the edge of life and death, he struggled to survive with a small Moonlight Fox he captured. When he finally escaped the devilish foremen on his island, he couldn’t help but let a breath out. But little does he know, the experience was only a beginning to a fated journey with his little Moonlight Fox…