One Piece: Became King of the World - Chapter 448 - 449: Ace VS Crocodile

Xuanyuan was reborn into a strange new world where training to be a Xian was a cornerstone. There was however something ancient dwelling inside his body. He could now devour all of creation…

This is the journey of an ordinary boy and his transformation into the supreme being that reigns over all existence! Everywhere he went, he could not help but tie his fate with numerous women. It did not matter whether they were a goddess or a devil…

- Description from Novelupdates

This was a fragmented and disorganized world, this was a place that had been forgotten.

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.

Arthur Morgan is an ordinary adult who ended up in the chaotic Marvel universe.He just wanted to be a discreet writer and make money from his books.It also has a 'cheat'.A daily login system.As the name suggests, whenever he logs in once a day he gains something from the system, ranging from skills to completely useless items.…One day, Arthur found a blonde girl passed out at the door of his house.“Why the hell is there a girl passed out on my doorstep!?”