Reincarnation: My All-Round Sweetheart - Chapter 10 - : The Magical Computer

In the whole world there lays twelve paths to climb the Tower of God, and in legends these twelve pathways leads toward legendary road of immortality. However these paths in the Tower of God, are far too long, without end.

“Hero, where are you going?”“To eat.”“Hero, where are you going?”“To the bathroom.”“Hero…!”“…”The woman who followed me everywhere… Ended up following me all the way to Earth.———A former hero who returned to Earth, now unemployed and just lazing around at home.Then, the saintess who came with him made a suggestion—“How about streaming?”“Hmm… This might actually be a good idea.”And so, the Hero & Saintess Healing Stream begins!

"Your bed is cold," spoke a voice in the room that had her eyes go wide in fear. Nervously, she turned around, gulping softly to see a shadow on her bed as if someone laid down there. The man who had been lying down sat up emerging out from the shadows where he had been waiting for her.

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.