One Piece : Roger Is My Vice Captain - Chapter 27 - Successfully infiltrating

Betrayed by his own werewolf clan and left to die in a forbidden vampire crypt, Lucien Drake awakens something ancient—something monstrous.His blood ignites the Crimson System, binding him to a long-lost vampire bloodline rumored to be more powerful than the vampire lords and deadlier than any alpha.Now reborn as a hybrid of vampire and werewolf, Lucien gains powers no being should wield. The System whispers, hungers, and rewards him for one thing: domination—of bloodlines, enemies, and women.With every kill, he evolves. With every seduction, his power multiplies. And with every conquest, the world bends closer to its knees.But ancient forces stir. Vampire princesses, werewolf queens, and dark priestesses all want him… dead, bound, or in their bed.In a world where the strong rule by blood, Lucien is rewriting the laws of nature—and he'll either claim the throne of night...Or drown the world in crimson fire.> “You think I'm a monster? You haven't even seen what I become when I climax with your queen.”

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.

Zhang Ruo Chen was the sole male heir of one of the nine emperors of the Kunlun Field. Ruo Chen’s father was known to all as the “Enlightened Emperor”, however Ruo Chen didn’t just leech off his status as emperor’s son. He proved himself to be a dragon amongst men, possessing a heaven defying body, and managing to cultivate to Greater Perfection within the Yellow Horizon Realm, at just the young age of 16.

But even though he stood at the summit of the younger generation and had a boundless future, he sadly died at the treacherous hands of his own fiancee at a young age.

Reincarnated 800 years later in the body of a young boy who shares his name, he found out his former fiancee already unified Kunlun’s Field and built the First Central Empire, and was now known as Empress Chi Yao… Empress Chi Yao—Her Majesty governed the mortal world and enjoyed prestige in all directions as well as an eternal life.

Zhang Ruochen stood outside of the Imperial Ancestral Temple, looking at the statue of Empress Chi Yao, and the flames of hatred burned in his heart. “After I practice for 13 years, I shall send the empress to her doom!”

- Description from Novelupdates

When gods gather, lightning will strike and the earth will move. Immortals! Which of the numerous way to immortality should one follow? Immortals are hard to seek, but why should immortals hide? Heaven has no mercy, but humans have emotions, and these emotions hinder the road to longevity!

Train the inner self to stay calm, train the external body to be resistant, then cross the three continents and four seas alone, and fight valiantly with demons and devils! With the heavenly baton in hand, raid the devils and demons without any resistance! Take one step to cross nine stars and chase the sword in the dreams! Traverse a thousand li of river and mountains in a single day! The exceptional beings do not mix with the ordinary! Within the universe, where can one find an obstacle! Moving like a dragon, with talent like a phoenix! The heavenly Daos and stars will guide one’s way!

- Description from Novelupdates