Reincarnated as incubus: I didn't mean to seduce you! - Chapter 3 - 1: Reincarnated as an Incubus, Show Your Real Skills in the Game World_

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.

Ruel finds himself thrust into a brutal post-apocalyptic world, bound to a bizarre “Milf System.” This system demands morally questionable acts – NTR, seducing milfs, and claiming other men's wives – as the sole means of gaining strength and essential survival skills.The brutal reality of this new world awakens Ruel's hidden lust and dark desires. He swiftly abandons any semblance of morality, embracing the system's perverse demands with growing fervor.Driven by an insatiable hunger for power and pleasure, Ruel revels in the ravages he inflicts, using his newfound abilities to dominate and conquer.His journey transforms him into a ruthless force, where survival is intertwined with the satisfaction of his darkest urges, leaving a trail of broken relationships and conquered women in his wake.

One day, Yoichi who grew up while not knowing his parents has received the news of his father’s death. His father left behind a testament——which said he is to pick only one out of five ‘little sister candidates’?!