Heroine Netori - Chapter 33: 18+

To save a doomed fantasy world, I killed the main characters, then destroyed the game world, and fell into another timeline as the academy's top seat and rival to the protagonist.Now, I'm trying to save the world and steer it towards a better ending…But I'm the final boss.

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.

After crossing over into the game world he had played before, Su Nan finds himself as a nobleman who has lost his title. At this time, the continent is still a barren wasteland of elements; powerful wizards abandoned this world a thousand years ago to explore the multiverse, becoming little more than elusive legends.Only Su Nan knows that, a thousand years later, the elements will revive, the wizards will return, and the continent is about to enter a prosperous era of magic.So, his task is quite simple: work hard to cultivate and become a wizard, surviving until the age of wizards arrives!“Resource-poor?”“There’s nothing for it; I’ll just have to synthesize everything myself.”Su Nan opens the synthesis cube. This is the story of a traveler with a player panel and a synthesis cube, leveraging a slight advantage of foresight to make a name for himself in a foreign world.

The eldest son of the assassin aristocrat Tuatha Dé.

The skill, experience, knowledge of the previous life, magic, all of which grows his power as an assassin.

Excellent assassins pass through. He was usually admired as the ideal lord, and behind it wielded a blade as an assassin aristocrat.