Ryuu Kusari no Ori -Kokoro no Uchi no “Kokoro”- - Chapter 6.05

An underprivileged prodigy, a cruel, ruthless world, and an epic story of battle and conquest. A young man with an exceptional inheritance leaves the small, rural city from which he hails on a journey to find the girl of his dreams. He defeats countless prodigies, sweeps through all forces that dare to stand in his way, and progresses step by step toward the pinnacle of all the worlds!
“I’m not targeting any gods in particular. All I’m trying to say is that all gods are trash in my eyes!”

- Description from Novelupdates

Kujo Yuuri, who had been playing Elysia Online, finally changed her occupation to the sage of her desire. Then, she was asked whether to go to the true Elyasia or not and selected [Yes], and somehow went to another world. Furthermore, she became a small child.

The small sage Yuuri and her companions’ love and adventure fantasy.

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.

Soaking in lava, sleeping in an Ancient Killing Formation;

Traversing alternative worlds in a heavy armored vehicle;

Riding a Gundam Sentinel and slaying immortals with Godzilla...

I got myself a stat system, and from then on, I only beefed up my defense!

I just can't help it, I'm afraid of pain! The Daluo Golden Immortals of other worlds are all really fierce, and all of them know super ultimate move with infinite power. They have little meetings every day to discuss how to break through my defense.

I really don't know why they're so obsessed...XD