I Was a Sword When I Reincarnated (WN) - Chapter 771

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 cold and homophobic top matched with a person he hated on a dating app, and discovered that the other was even more clingy than he thought!

After breaking up with his girlfriend, he accidentally acquired a genius system and rose from there against the heavens, becoming invincible..

- Description from Novelupdates

Jun Xiaoyao was transported to a mystical world and became the divine child of a Clan of the Ancients. He came to possess an invincible background, unparalleled talents and even a check-in system, enabling him to acquire an Accomplished Sacred Body of the Ancients at the very beginning of his new life.

He acquired the Divine Elephant Overpowering Force, a six-star reward, checking in at the Old Tablet of Taiyue.

He acquired the Bones of Supremacy, a seven-star reward, checking in at his Ten Years Old Banquet.

He acquired the Cauldron of Maternal Qi of All Beings, an eight-star reward, checking in at the Bronze Mystical Hall.

He acquired the Grand Method of Freedom Melding, a ten-star reward, checking in at the Borderless Ocean.

He sat on the clouds countless years later, with his sword pointing at the heavens, saying, “I alone shall rule over the heavens and the earth. I shall become the pinnacle at the very end of the mystic path!”

- Description from MTL