Re:Zero Kara Hajimeru Isekai Seikatsu - Chapter 78Arc 7, - “A Volatile Reunion”

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 Ye Qing Ran wakes up, she finds that she has transmigrated into a book. She has become the vain, domineering, and evil villain who dies a tragic death.

Unable to control his mouth, Lin Jian Yin scared away eight previous girlfriends and six previous managers thanks to his poisonous words. Finally unable to stand it, he goes to a strange antique shop recommended by his friend. The shop supposedly has something that can help him.

Even though a Nintendo that plays cartridges is a bit outdated, and probably no one plays it anymore, isn’t it too exaggerated to place it in an antique shop to sell?

After returning home with a Nintendo, Lin Jian Yin inserts the cartridge that the owner sold to him at a huge discount. Only then does he discover that this is actually a simulation game. The female protagonist isn’t a cute loli, nor is she a mature woman. Rather, with her old lady hair and blue-white slippers, she is such a frightening woman that calling her a Taiwanese babe would seriously be insulting Taiwanese babes.

Gods! His mission is actually to help this woman marry a perfect prince! How is that possible!!!

Wait, as the main guy protagonist, Lin Jian Yin actually isn’t the prince. Then, then, who exactly is he… No, “what” exactly is he?

The Blood Warrior of the Ungpae Association, who created a sea of blood wherever he went, made the world of the Forces of Evil possible.

The Nine Great Sects and the Six Great Clans joined forces to fight him, but were unable to stop him.

Four Great Warriors, who were Murim’s last hope, appeared.

The four of them fought against the Blood Warrior and eventually defeated him at Mount Song.

The time has come for the legacy of the Blood Warrior to rise once again.