Loser's redo: Transmigration in a novel - Chapter 133 I Need Strength...

A continuation from where High School DxD Volume 25 left off.

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.

After losing his parents to an accident, Haruto is thrust into a state of depression. Realizing he never had the power to change things, he eventually took his own life. Before moving on, he’s selected by beings greater than his understanding to balance out a world suddenly facing peril. The world of Mordell, where demon-like creatures and beasts roam, and Guilds of ability users called Warlords are the force to combat these creatures. Armed with the power to change things, he has the choice. Continue living in despair or accept his second chance and become a true Warlord.

There are all sorts of lunatics in the world:Self-centered, reckless, psychotic, impulsive, obsessive, and pe*verted.As far as Suin knows, that man embodied every single one of those traits—an obsessive, pe*verted psycho.And now, that lunatic is back.“Finally, we meet.”“Adult Lee Suin.”He didn’t even try to hide the sticky hunger in his gaze, like a starved lion finally spotting its prey.“A job reassignment?”“I want Lee Suin to help me.”Chairman Woo Ilhwa, unaware of his son’s true intentions, reassigns Suin, his chief secretary, to serve as his son’s personal secretary.This forces Suin into close proximity with the man who’s been preying on her from the shadows.“Wait for me, Lee Suin.”During his eleven years of exile, Jaehee had dreamed of one thing:A proper relationship—not as a restricted minor, but as a full-grown adult.A relationship where he could take what he wanted, whenever and however he pleased.That’s why, even though Suin was as rigid as a steel rod, his sly persistence ignited the spark within him whenever he faced her.“What do you want from me?”“You.”“Lee Suin.”But it seems Suin has been flirting with some bastard behind his back, and Jaehee’s jealousy and obsession explode.“Don’t take a single step.”“Unless you want to see me go completely insane.”What nonsense.You were already insane to begin with.