The Retired Hero is an Extra - Chapter 139 - : Not My Problem

In Academy City, magic and science coexist in an unwavering power struggle. Toma Kamijo, an academically-challenged student in Academy City, wields the power of the Imagine Breaker in his right hand, which allows him to completely negate all supernatural powers – as well as his own luck. When he happens upon a mysterious nun named Index, whose mind has been implanted with the Index Librorum Prohibitorum – 103,000 ancient texts banned by the Church – Toma’s luck is about to be pushed to its limits when he finds himself in the middle of a war he never expected!

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.

[Congratulations, you have earned +9 coins. You have repaid 999,999,999 / 1,000,000,000 Coins. You need 1 more coin to repay your debt.]“You’ve got to be kidding me.”______After living a hundred lives, Lucian finally managed to repay his debt to the system. World after world, he fought, bled, and struggled—all for the freedom he had foolishly given up the day he begged the system to save his life.At last, he had done it. 999,999,990 coins. Just one more mission, one last world, and he would finally be free...Or so he thought.But this was no joke. The system had screwed him over one final time.Still, there was hope. With only a single coin left to repay, the system could no longer play its tricks. Freedom was just within his grasp—if he could survive this last world.All Lucian had to do was reach the end. Simple, right?Except this time, the world itself seemed determined to destroy him.

As part of the imperial family, every move by Chu Yuan in this game of chess is made with apprehension, fearing that with a moment of inattentiveness, the whole match will be lost in a single move. Ascending to the throne at eighteen, not half a year passes before civil strife erupts in Yun Nan. Though the thoughts of the old guard at the imperial court are not exactly identical, they are all waiting to see how the new emperor will put an end to this. Unexpectedly, before this side could make a move, a few thousand miles away, the King of Xi Nan, Duan Bai Yue, had already personally commanded troops to attack in all directions; not half a year had passed when peace was restored. Sparse moonlight shines into the palace; Chu Yuan stamped the wax seal himself, and had a secret letter sent urgently to Yun Nan 800 miles away — this time, what must we(1) give in exchange? Brush marks passed through the back of the paper; it almost can be seen, when writing this line, how angry the young emperor was. Duan Bai Yue spread out a piece of paper unhurriedly, replying with only one word. You.