Toaru Majutsu no Index: New Testament - Volume 10, Chapter 18: V.S. “The One who Opposes the Magic God” Round_10.

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

I became a scientist for an evil organization.…But I’m too competent.

Lacking a pocket dimension, lacking a power, lacking a thigh to hug onto and the three life advantages (money, power, and looks), he had been cautiously living in the apocalypse for ten years, getting closer to falling inside the zombie’s mouths. But unexpectedly, he had the terrible luck, to be caught in a fight between two gangs and die, it really left people feeling disappointed.

But when he opened his eyes, he had returned to a decade ago, three months before the apocalypse!

Like before he still lacked an ability, an ordinary person without a pocket dimension, but he did have ten full years of experience living in the apocalypse! Even if he didn’t fight zombies, didn’t hunt monsters, he could still live a carefree farming life in the safe zone.

Find a safe house, utilise all kinds of skills from his previous life to farm in exchange for meat, and if possible, find a person to peacefully spend the rest of his life with; ordinary people had their own ordinary little pieces of happiness.

Originally believing he had picked up a beauty he returned home to prepare a golden house, but on the contrary he was the one being pushed down……someone once said, whether it is people or matters, by no means can you only look at the surface!

- Description from novelupdates

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.