MTL - Princess too Young, Prince too Old - Chapter 1174 Don't worry, my dear

Xiao Yu transmigrates into a comprehensive xianxia universe, becoming the senior brother of Tianyong City and activating the Immortal Emperor System. Starting from the Foundation Establishment stage, he ascends through the Golden Core, Nascent Soul, and Spirit Transformation stages, ultimately achieving immortality! This universe seamlessly integrates multiple xianxia classics, such as Chinese Paladin 1, Chinese Paladin 3, and Gu Jian Qi Tan, among others.

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.

When an era came to an end, various forces set foot in cultivation to compete for immortality. A young boy who spent most of the time sleeping got lucky in the troubled times and became an unparalleled immortal who could cover the sky with a snap of fingers. Was he going to live forever?

- Description from Novelupdates

In a modern world, a professional assassin was murdered by her beloved and found herself revived in an ancient world as a general’s daughter with a weak physique. She was engaged to a prince, but because she did not have a nice appearance, her fiancé and sister attempted to kill her. Although she had to struggle to survive, there were also those who unconditionally loves her that supported her in her time of need.