Akuyaku Reijou ni Nanka Narimasen. Watashi wa『Futsuu』no Koushaku Reijou desu! - Chapter 215: Cidar-kun’s father.

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.

Once feared as the Queen of Shadows, Eydis now faces her greatest humiliation: high school.Stripped of her magic, her kingdom, and (most insultingly) her dignity, she’s stuck in the body of a weak, whiny teenager with no power, no allies, and no money. And her terrifying familiars? Complicated. Her new greatest adversary? The Maths teacher.And we certainly can’t forget about that giant, pulsating eye watching from the heavens (debatable), ominously known as… The Eye… (I know, right?) that threatens to tear apart her new reality.But one thing Eydis hasn’t forgotten: shadows always trail after you.The real question is whether she’ll stand in them once more as their queen… or be swallowed by them, piece by piece.“Royal Reboot: Level Up, Your Majesty!” - a comedic dark fantasy where nothing is as it seems and every choice could be her last.A/N: Action/Romance/Slice of Life/LGBTQChapter updates weekly, weakly.While the story has a comedic undertone, darker themes are presented.

What happens when you transmigrate to Beast World? With the system in hand, the world is for your taking! One day, Su Tang, an intern at the hospital, is struck by a system and transmigrates to Beast World. It's a wondrous world with winged tigers, fire-spitting birds, and enticing man-eating flowers… Everything in this world leaves Su Tang awestruck!After the Chief of Winged Tiger Tribe saves Su Tang, she learns how backward this place was. Su Tang is determined to help change the world! Under the system’s guidance, she helps to extract salt, build homes, dig traps, make weapons and store food for winter… And perhaps even save the world while she's at it!