Dungeon of Niflheim - Chapter 76

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.

Passing through the world after nuclear war on Earth, all humans fall into a game called “Transcendence”.Through games, people can gain the power to move mountains and seas. The strong can cross the void or the universe and do anything they want.Stel had been in this otherworldly place for eighteen years when one day, he woke up with the ability to “Evolve Every Day.”Various talents?Evolve!SSS-class “Descent of the God,” all attributes doubled, resurrection from death.SSS-class “Soul of Arcane,” all magic cast without conditions, power doubled, ignoring the opponent's defense.What about different skills?Evolve!“Fireball” → “Flamestorm”“Wind Blade” → “Storm of Death”...And what about different professions?Evolve!Treasured items? Evolve!Pets? Evolve!By the time Stel stepped out of the gaming pod and back into reality, the entire universe was already at his feet.

Crossing to One Piece world, he became Roger’s younger brother.

Unexpectedly, Gol-D-Roger who was in his fifties had a teenage brother. But he was so weak.

Fortunately, at the age of sixteen, he actually found himself with a possession soul system.

He had attached to the master IP man, also to the White Phoenix and to Ge Nie with his strong ability of the Hundred Step Flying Sword.

If you think that he can only Purchase these? Then you’re wrong!

Pain, Itachi, Ichigo Kurosaki, as long as there is money, any soul can be Purchased.

- Description from Novelupdates

She, a 21st century mercenary queen, had crossed over into a tragically betrayed body of a waste. Waste? She will show them what it means to be a waste! Betrayed? With the Ancient Manual in her hands, she will astonish all the despicable men and cheap women!

Wait! Didn’t everyone say that she was an evil woman which everyone feared? Why is his Third Highness, full of mystery and charisma, so interested in her?

- Description from Novelupdates