One Piece - I Am A Different Luffy! - Chapter 421 - 420 - Return to Skypiea.

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.

Orion was on his way back home from work.He was hurrying back home to take a nap while planning how he would spend his weekend as well, but while he was lost in thought, a truck suddenly appeared out of nowhere and the last thing he remembered was the truck barreling towards him before everything around him turned dark.However to his surprise, he didn’t feel any pain after having the accident. In fact, he couldn’t see anything.Everything around him seemed dark but when he opened his mouth to speak, he heard the gurgling sounds of a baby.Noticing that the one sounding like a baby was him, Orion tried to open his eyes to know exactly where he was, but when he did, the first thing his eyes fell upon was a stunning beautiful elf, holding him with the most tenderest of care.Not only was she his mother, she was also a queen as well and she had a beautiful sister who adored him just as much as his mother.Aside from this, Orion also noticed he had received a system which allowed him to grow and evolve faster than a normal High Elf but after finding out the huge role his mother played in eradicating the war between all races, Orion vowed to live a happy and fulfilling life with his mother, aunt and a few others he cared a lot about.

【Substitute Marriage+Adorable Baby+Sweet Pampering+Both Leads Pure+Chasing Wife Drama+Anti-cliché+Face-slapping Revenge】A conspiracy, Ivy Kensington marries in place of another to the powerful Master Blackwood.During the day, she is his most disliked humble maid.At night, she becomes his bride, sharing intimacy every day.When the secret of the substitute marriage is revealed, Ivy Kensington takes her child and flees far away, only to be pursued relentlessly by the man: “Ivy Kensington, you can only be mine!”She pleads, struggles, yet cannot escape the cage the man has crafted for her.Four years later, Ivy Kensington returns with a stunning appearance and child, “Master Blackwood, long time no see.”The man becomes a doting husband, pampering her beyond measure: “Be good, call me hubby!”