Omae wo Onii-chan ni Shite Yarouka!? - Volume 3, 7th of May, Tuesday.

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.

Born and raised in a lab Tristan must figure out how to live and survive in the outside world. To make matters worse he has 4 others to look after. He's the oldest but is always being taken care of, to make sure his lab siblings want for nothing, Tristan will need to make a difficult decision. The goal is to provide for his siblings but he ends up living just like he was groomed to live. On top of everything else, there are four alphas who want to mate with him, and they don't mind sharing. Will Tristan accept his fate? Or will he runaway?

Satou Shiki a Japan present-day university student suddenly one day he got attacked by a slasher when he open his eyes he was already transferred to another world’s labyrinth city. In that another world he who was awakened to do a lot of “things”.

Encountering a car crash, the King of Silver Screen, Ye Sinian, was bound to a Cannon Fodder Counterattack System.

After reincarnating for hundreds of lives, he has finally earned enough “travel expenses” to go back home.

However, he didn’t think that the system would suddenly malfunction, making returning back home from then on hopeless.

With the shackles of a millennium broken, Ye Sinian aggressively counterattacked!

Reversing fates while hugging the mentally ill* Lord Seme, he walked towards the apex of humanity!

*Mentally ill – Schizophrenic

- Description from Novelupdates