Akuyaku Reijou ni Nanka Narimasen. Watashi wa『Futsuu』no Koushaku Reijou desu! - Chapter 186.2: The truth about Wolfanea.

I dedicated 10 years of my life, focusing solely on regression.[Authority: Death Regression has naturally been nullified.

“No way, Salino, you said that this little guy who killed 300 million pirates in one blow, who is only eight years old this year, is your biological brother?!”

Sengoku Marshal’s office, Akainu, Aokiji, Garp, Sengoku, Crane, all looked confused. “It’s really him!”

Huang Yuan was also shocked and confused, his younger brother was obviously only eight years old, how could he be so fierce? ! At this time, summer is here. Sengoku invited him to join the navy.

“Joining the navy is no problem, I want to be an admiral!”

Red Dog frowned: “General? Just you?” Xia Tian made a decisive move, and sent Red Dog flying with one punch, shocking the audience!

“Yes, it’s just me.”

- Description from novelbuddy

After successfully reaching the Core Formation Stage and forming his Golden Core, Bai Langtian was betrayed by his own Master. His core was ripped from his body, and he was thrown off a mountain cliff into a valley full of demonic beasts.Thankfully, he survived the fall, and met his senior sister, Shangguan Yue Ling.She too had been betrayed by the same Master and pushed into this valley ten years ago. Ever since, she had been surviving alone by eating the corrupted flesh of demonic beasts.Now, Yue Ling revealed to Langtian a new path of cultivation:Demonic Cultivation.To reclaim his strength and take revenge, he must consume the flesh and essence of ten thousand demonic beasts.

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.