Reborn and Counterattack: The CEO's Powerful Sweetheart - Chapter 1 - 00: Death of the Widow

In a Fantasy world in which a young girl with the Divine Protection of the Hero battles against the Demon Lord. In that world, Red, the elder brother of that young girl Hero, possessing the Divine Protection of the Guide which only grants a high initial level, fought in the initial party of the Hero.

Spot was summoned from his comfortable charging pad and familiar floors to a world of magic and intrigue. After the flight of his new patrons, he is left to care for a filthy castle. During his quest to keep this new home clean, he will face demons, foreign armies, and the dreaded stairs.All those who stand before him will be swept away. Those who follow his spotless trail will find enlightenment, purity, and a world on its knees.Follow this wholesome vacuum on his quest to power.

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.

The Third World War has been ended by the efforts of Kamijou Touma. With that, he vanished. With the Magic Side regrouping, the Sabbath for their followers has arrived.

In the headquarters of the Science Side, Academy City’s strongest Level 5 Esper Accelerator has washed his hands off the “Darkness.” Along with Last Order and Misaka Worst, his days pass by peacefully with no sign of GROUP.

Hamazura Shiage has formed a new ITEM with Kinuhata, Takitsubo and Mugino. Peace has come to the hands of the alumni who have “graduated” from Academy’s Dark Side at last… at least until a new evil “first year student” appears before them.

— This is a follow up to the popular Toaru Majutsu no Index light novel series, where Kamachi-Sensei has promised to deliver new premises and give a totally new flavor to the fights and plot developments