Steel, Explosives, and Spellcasters - Chapter 14 - 7: A good soldier is one who can grab a weapon and has saliva in his mouth.

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.

Today, I am a substitute for your fiancee. Tomorrow, I’ll become your sister-in-law!

Mu Mingtang is the substitute of the male lead’s first love. After she lost her family, she was adopted by the Jiang family and eventually became engaged to the male lead, the Prince of Jin.

Understanding very well that she was only a substitute, she removed her claws and fangs and turned herself into an imitation of the Prince of Jin’s first love. She couldn’t speak or laugh as she wished, she was prepared to live in the shadow of another woman for her entire life… until one day, the real Miss Jiang returned.

The real Miss Jiang was reborn. When she learned that she was the male love’s first love, she immediately returned to fight for her engagement and identity.

In order to please his first love, the Prince of Jin gave the substitute to the Prince of Qiyang, who had become a dying madman. She was just a low-quality fake, anyway. If she dared to anger his first love, he would turn her into a childless and powerless widow for the rest of her life.

Mu Mingtang, the target of their mockery, finally snapped: Okay, since you gave me to another man, I’ll make you bow and call me sister-in-law!

However, none of them expected the Prince of Qiyang, the God of War, to actually wake up!

—

Xie Xuanchen is the son of the late emperor. The whole world once trembled beneath his feet, but one day, for a reason unknown to even Xie Xuanchen himself, his nature suddenly changed. He became cruel and bloodthirsty, leaving his father with no choice but to pass the throne to his uncle.

Eventually, Xie Xuanchen was unable to resist the illness and fell into a coma.

When he woke up again, there was a beauty standing before his bed, looking at him in surprise. Then, for the sake of his domineering little princess, he revived his name as the God of War, reclaimed the throne, and united the world.

I once captured the world to satisfy my own ambition. Now, you are the reason for my ambition.

After looking at a handsome man’s picture, he has transmigrated into another world. Rong Yi looked up at the sky, speechless. How unlucky could he be to have transmigrated into a loser + sissy’s body…

What’s worse, the original master of this body has been married to a man! And the worst thing is…

Rong Yi takes a deep breath and lowers his head to look at his chest! Flat! Check! Then he pulls open his pants and luckily see his ‘brother’ is still there, feeling much relieved…

He said to the little cute kid, “What did you say? Say it again.”

…

Crossing to One Piece world, he became Roger’s younger brother.

Unexpectedly, Gol-D-Roger who was in his fifties had a teenage brother. But he was so weak.

Fortunately, at the age of sixteen, he actually found himself with a possession soul system.

He had attached to the master IP man, also to the White Phoenix and to Ge Nie with his strong ability of the Hundred Step Flying Sword.

If you think that he can only Purchase these? Then you’re wrong!

Pain, Itachi, Ichigo Kurosaki, as long as there is money, any soul can be Purchased.

- Description from Novelupdates