The Regressed Demon Lord is Kind - Chapter 478

Max died right after beating an impossible level in his favorite RPG, Eldoria's Entry 3.That should have been the end.Instead, he woke up inside the game.In a world where humans do not exist, Max reincarnated as one.With miserable stats and no way to grow like a normal adventurer, he was labeled completely useless from the start.His only saving grace was a unique Rank-SSS skill.Unfortunately, he didn’t really understand how it worked.Before he could figure out how to survive, Max opened his eyes inside a royal castle.It was an elven princess’s birthday.And he was her new pet.----------------------------------------------What To Expect:-NEW CHAPTERS ALL DAYS-A system that isn’t always well explained-Humor of all kinds.-No harem-No R18.-OP MC.-Slice of life moments to slow things down.-Adventure moments filled with danger and tough choices.

I gave them my everything.My time… my strength… my heart.I trained while they slept.I smiled when they laughed.I stayed… even when it hurt.And what did I get?Nothing.They looked at me like I was pathetic.Like, I didn’t belong.Like I was… less.But I... the naive person I am, continued trusting them.They told me to act like trash, fine—I became trash.They told me to act like a scumbag, fine—I played the role.However...One mistake, one single moment...That’s all it took.And they threw me away.But now…Someone else woke up in my body.A stranger, a man who doesn’t know the pain I suffered, but wears my face.Let’s see what he does with it.Because me?I’m done with this life, so to the soul who took over my body...This is your mess now…'Gray'.

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.

He swore that if he was given a second chance to live, he would live his life to the fullest.His life was full of misery but he was reincarnated in the body of the son of the strongest expert in the empire.He had the looks, wealth, and women. He was known as the “Handsome Playboy” and he didn't want to become a righteous protagonist.He awakened a system that can make him strong by making others feel the 7 sins towards him.He will collect many beauties and live to the peak of life.