She's a Passerby, But Can See the Protagonist's Halo - Chapter 100

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.

[Scanning completed][Host detected. System activated]“What's going on?”[Host, I am the system. I will help You Build Your Empire. You have arrived in a world called Proxima Center. It is 10 times bigger than your planet]In This story, we follow the life of Alberto, a World War II veteran who was killed in action during the war.But God decided to give him another life. He sends him to a fantasy world. This fantasy realm is ten times the size of Earth, teeming with legendary creatures and vast nations that rival even the might of the Mongol Empire. Where our main character will build his country entirely from scratch using the system given by God. A powerful system that is capable of making him a powerful beingSo let's enjoy our main character's journey together.Join Alberto on his epic journey as he transforms from a soldier into a sovereign, building alliances, facing formidable foes, and perhaps even discovering love amidst the chaos.

Transmigrating to a lawless person and then directly upgrading to a little brat’s stepmother. Xiao Ting said, “Crap, there’s no need to even give birth to a child. God, I love you so much …”

- Description from Novelupdates

Qin Chen crossed into Taiyi Holy Land as a sweeper, and at the age of sixteen awakened the system. As long as he signed in at different places, he could get different rewards.

Sign in at the Land of Emperor Ruins and get the world’s No. 1 Chaos Holy Body and the Chaos Emperor Sutra!

Sign in to seal the magic land and get the quasi-emperor soldiers!

Sign in at the Refining Hall and get the God-level Refining Technique!

Sign in at the medicine garden and get the medicine of immortality!

Sign in at the Imperial Palace and get the Emperor-level forbidden magical power ‘Resurrection from the Dead’!

…

Qin Chen thought that he would just sign in silently until the world was invincible.

One day, the relics of the Great Emperor will appear in the Holy Land, all the holy places, families, and ancient dynasties have come, and there will be an unparalleled demon king in the relics, killing countless powerhouses, ruling the world, and wanting to destroy the Holy Land.

In desperation, Qin Chen could only walk out, slapped the Demon King to death, and sighed: “I just want to be a sweeper and sign in silently. Why do you force me to take action?”

- Description from novelbuddy