Rebirth of a Billionaire Heir - Chapter 8 - : Chloe’s Counterstrike

One day every human on the world suddenly receives a mail claiming to enact the World Salvation Project. Half in doubt Kurosaki Shion, a diligent university student and loner, follows the mail’s instructions, becoming one of a million Demon Kings governing his very own Domain in the new world.

*** This is a post-apocalyptic story containing many fantasy elements. It is a somewhat dark tale following Shion as he grows while aiming for the unification of the all too sudden new world. It has many game-elements bolstered by strategical thinking while at the same time providing funny moments and romantic encounters.

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

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.

5 years after the world changed, the final boss appeared.