Starting with Growing Mushrooms - Chapter 429 - 332: Changes, a New Terrifying God Calamity

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.

A world where mana density was extremely abundant. Because of that, the world connected to a special place through an ancient gate—the World of Beasts. Through this connection with beasts, mankind became superhuman, wielding power capable of tearing apart sky and ground.However, too much of anything is never a good thing. Countless dungeons appeared across the rifts… and demons.Rocky Stephens, the first son of a Great Clan, the reincarnator, carrying memories from another world.… yet also a useless piece of trash. No one even remembered his name. His parents died. Betrayed by the branch clan, his beast was killed. He lived in a phase he had never dreamed of—a nightmare.When a second chance came, he returned to the World of Beasts… and awakened a system that could see through all Beasts’ training paths!With the system, his beast could level up like the wind… it could learn and upgrade its skills on its own, and even more.

Sealed Kaguya;Mikoto on her wedding night;Kushina during the Nine-Tails' Rampage;Kidnapped Konan...Uchiha Kage, who crawled out of the pile of dead bodies from the night of the clan massacre, discovers that every night he can enter a mysterious space.The space not only contains real female ninjas, but also real instances that update from time to time.Furthermore, by absorbing the dropped ninja fragments, he will also gain the abilities of the corresponding ninja.Crap, it's like I've started playing in the real Naruto world!You say I'm inherently evil?That's right, from now on, I am the most evil Uchiha!I'm going to make Konoha... No, I'm going to turn the entire ninja world into a paradise that belongs to only me!——Sasuke: I treated you like a younger brother, but it turns out you're my dad?Naruto: Awesome, Sasuke! Turns out we're actually blood brothers!