How To Ruin A Love Comedy - Chapter 25: Not Hanazawa, Miyuki.

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.

Who needs a Class when you're already the strongest anyways?Ten years ago, Amelia woke up alone and lost in a broken world where she had to fight for her survival.Now, after reaching the pinnacle of power, defeating the Void itself, and escaping the abyss, she has finally found her way back into the real world. But instead of returning to Earth, she arrives in the land of Vacuos. A fantasy world with magic, monsters, Classes, and Levels. A world that is governed by a System like it were a video game.And when rewarded with a Class befitting her accomplishments— to become a powerful [Hero] that will forever dedicate her life to protecting this world that is not her own— she only has one response.“Absolutely not. I’m going to live a normal life now, thank you very much.”

This is the 40,000th year that the Empire has ruled the Milky Way. The glory of the Great Crusade has long been lost in the dust of history. Su Yu traveled through time and opened his eyes to see the ruined planet in front of him, with a confused look on his face.

On this planet, there are extremely dilapidated war machines that stretch for thousands of kilometers, alien behemoths whose roars can shatter mountains and rivers, and radiation that can cause further damage to the surrounding environment just by moving. Alien beast——

There is everything here except hope.

Regardless of whether he wanted to or not, Su Yu, who had struggled to survive for three years and was inevitably infected with radiation sickness in the end, seemed to be one of the desperate people.

Until his career panel, which allows for unlimited career changes, was finally opened.

“Ding!”

“It is detected that the host has met the prerequisites. Do you want to take up the occupation [Mechanic]?”

“After completing this profession, you can gain professional experience and improve your professional level from daily maintenance, recycling, and assembly of mechanical creations. With each upgrade, you can gain an increase in physical fitness…”

Looking at the old gun parts piled up in his repair room, Su Yu’s eyes lit up like never before!

Many years later, at the core of the empire, at the highest point of the Terran world, the mechanic from the Ruined Star, the Ghost Shadow Blade of the Dead Wasteland, the restarter of the Titan Weapon Plan, the Governor of the Broken Star Territory, the Lord of Mechanical Ascension, the Supreme Throne of the Forge World, Su Yu looked at the torrent of steel coming from below and waved his hand to give the order!

[Our goal is to make the (second) (crossed out) empire great again! 】

- Description from novelbuddy

Akira Kisaragi traverses into the Bleach world, unlocking a check-in system.He initially thought that by checking in daily, he could become stronger, soon become the Captain-Commander, join Division Zero, punch Yhwach, kick the Soul King, and marry Unohana...However, the system's style wasn't quite what he had imagined.〈 Check-in complete, obtained Genryūsai Yamamoto's secret roasted sweet potato! 〉〈 Check-in complete, obtained exclusive attribute: King of Normal Attacks, effect... 〉〈 Check-in complete, obtained Retsu Unohana's... 〉Akira's eyes suddenly lit up!“Seems like this might not be so bad after all!”