I Play Yu-Gi-Oh! Card Game - Chapter 1526: Sword of Victory

Gu Bai always believed that the stupidest thing he had ever done was listening to his bestie’s words of becoming a stallion genre novel writer, the most frustrating thing was that he changed the moral, smart, and healthy youngster, that he had decided on, into a big boss…but in the end, he discovered that the consequences of changing the original plot were more serious than he expected. Things like encountering the outrageous character he wrote with his own hand…

Oh·my·god! He freaking eats people! Right now, he can only turn devouring people into “devouring” people… maybe.

In short, this is a story about a dumb author who was the first to start a trend of human cannibalism in stallion genre novels, who in the end, was unable to escape from the whirlpool of destiny (not really).

- Description from Novelupdates

I returned to Earth as the invincible Knight King. But the Gods came with me.

Once upon a time, an Alchemist Grandmaster from the World of Immortals accidentally took possession of a playboy, who hailed from a rich and powerful family, and became a student in the middle of his midterms.

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.