The Sword and Heir of Shadows - Chapter 69: At what Cost.

Upon awakening in a parallel world, Lin Yi discovered that not only were Xiao Zhuang and Xiao Ying present, but also veterans like Old Pao, Tou Lao Gao, Qiangzi…He had unlocked an Entry Upgrade System.【Shooting Novice (White) → Hundred Paces Piercing Yang (Gold)】【Superior Memory (Blue) → Photographic Recall (Gold)】【Master of Struggles (Blue) → Supreme Titan of Competition (Gold)】【Martial Arts Grandmaster (Purple) → Mortal Warlord (Red)】【……】As time passed, Lin Yi steadily advanced towards the peak, growing ever stronger.Yet, as he ascended, unexpected figures began to emerge before him—He Chenguang, Xu Sanduo, Lei Zhan, Yan Poyue, An Ran, Long Xiaoyun, Shen Ge…Only then did Lin Yi realise that this was not merely the world of Special One, but a vast amalgamation of multiple special forces universes.

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 13-year-old deaf teenager living in the 21st century suddenly found himself as a young boy in Japan during the early 1900s. With two World Wars, two nuclear bombs, Hitler and many other disasters awaiting his future, he thought things couldn't get worse.Except it did.He found out later on that he had actually reincarnated into the world of Demon Slayer where man-eating demons ruled the night. He thought things couldn't get worse.Except it did.But hey! At least he had unparalleled talent, incredibly special eyes and future knowledge.How will the story of Demon Slayer change with the addition of this unique character? Will so many still die if the Hashiras had one more pillar in the final battle?Or will the story end on a much happier note?

Song Yu Xi is a tasker.

The system told her that she has a great and glorious task on her shoulders – to save the world!

Song Xu Yi is dedicated to her work, remembering the first rule of the Fast-Travel Code of “no love”, and is dedicated to reforming the world-ending villain and strengthening the power of the protagonist, but she never thought that every world would develop in an unpredictable direction:
The beautiful and charming villainous movie queen hugged Song Xu Yi’s neck and breathed like an orchid: “Kid, why do you always blush when you see me?”

The sickly and delicate villain Omega raised Song Xu Yi’s chin: “My dear Miss Song, how does it feel to have an Alpha become an Omega?”

The cold and beautiful villain student sneered and put the five million check into her school bag: “There is no other way to repay the favor of funding, only the promise of your body.”

The villainous prince disguised as a man slowly tore up the peace proposal: “If you want to negotiate peace, you can let your Grand Princess Song Xu Yi come and make peace…”
System （(艹皿艹 )）: Say no to love and don’t fall in love!!!

Song Xu Yi ((╥_╥)): Sorry!

I blame the villain for being too beautiful, I couldn’t see her tears…

The love story of a hardworking wage earner tasker and a gloomy world-destroying paranoid villain.

- Description from Novelupdates