I Became Invincible After Sweeping The Floor For 70 Years - Chapter 35

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.

Being able to see into people's past has no real appeal for the teenager this story is about, letting him use it only as amusement and to show off when he was drunk.Never watch into someone's past beyond a superficial level.Never try to find out more than you should.NEVER. EVER. LOOK. INTO. THE. FUTURE.But everything changed the moment he was forced to look into the future, was forced to investigate a murder, and was forced to make the acquaintance of the victim's twin brother('s fists).The more time passed, the more it appeared that the primary reason for this murder wasn't a local problem, but a global one.This single, marred corpse was the beginning of a threat that would shake the world.(MC looses a screw when he enters the prison)BL, first-person view; MC is shuo (perhaps even a reversible couple); love interest falls in love first; both MC and ML are straight, mutual bending, Enemies to Lovers

“There are no heroes. In life, the monsters win.”

...

In 2106, [Mayhem Online], a fully immersive VRMMO game, was released. Soon, it dominated the world's economy when people could exchange the in-game currency with real-life currency and vice versa.

In the year 2107, Flynn Grey, a 22-year-old college dropout with an ambiguous history, joined in the fray of billions of people that had already started playing [Mayhem]. Hoping to uncover the game's secret and earn a fortune, he spent months on adventures without fruitful results.

For better or worse, Shura, Flynn's in-game character, ends up in a great Wyvern's den, acquiring a hidden class and a monstrous race. Join him as he defeats his past and paves his way into becoming a true legend in both worlds.