Rebirth in One Piece as Deputy Captain - Chapter 583

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.

27-year-old Hisha, transmigrates into the body of a thousand-year-old overpowered supreme overlord who had everything at his disposal, except one–worthy companions by his side.

Hence, a tournament was held to choose the best out of the most beautiful, unique and strong women across the land.

These women don't follow the rule of coexisting women in a harem, they fight for the right to bed their lord and would stop at nothing but to use every opportunity to seduce, and fight on his behalf just to get his attention and favor.

Hisha never liked such a barbaric method of getting a companion.

'Why choose a few, if you can have them all?'

'If he can't have them all, he would try to work out coexisting the strongest for his pleasure and benefit.'

He realizes his 'Desire System' levels him up with every adoration gotten from his harem. The stronger they get, the higher his level and hold in his world.

As he continues to break his limits with the help of his harem, he finds out there are others that threaten his rule and the balance of his land.

'Let the tournament begin!'

“I hope you don’t fall in love with me, because I won’t be taking responsibility,” warned the young man. “Don’t worry, I won’t fall in love with a body double,” the employer dully replied. Yet, both of them forgot what they had said.

A broken prince, a shadowy scheme, all that amidst a bloody fight for a throne wrongly succeeded. Join a group of youngsters as they take their first steps into the martial world, towards the grandest adventure of their lives. It all begins in a certain inn, set against verdant mountains and facing a scenic lake.

“Bring us your finest wine and best meat!” Yelled a hulking man who seemed to be the leader of the dozen strong group.

“How much?” The waiter anxiously nodded his head.

“As much as you have!” The hulking man yelled back.

“That’s…”

“HUH?” The hulking man shot the waiter a furious glare.

“Dear guests, our inn operates on the principle of ‘pay first, dishes later’. As such, it will be better if you tell us exactly how much meat and wine you need.” Xiao Se returned their furious stares with a thin smile.

“Who are you supposed to be?” The hulking man eyed him with bulging eyes.

“This humble one is known as Xiao Se, the owner of this inn, the Fallen Snow Villa.” Xiao Se replied with the same smile and with a level of courtesy worth a solid 12/10.

“Well, we have no money.” The hulking man stabbed his blade into one of the nearby tables.

“Oh?”

“But I’m sure you have some!” The man pointed his finger at Xiao Se.

At that, Xiao Se furiously shook his head. “I’m sorry to break it to you but our little inn hasn’t made a single sale in almost a month. I’m about to owe them salaries myself…”

“Like hell if I care!” The hulking man smashed his palm down on the table. “Even if you have no money, that fur coat of yours should at least be worth a hundred odd silvers.”

“NONSENSE!” Yelled Xiao Se, eyes wide open and gaze as sharp as daggers.

The hulking man was stunned, his body even shivering involuntarily for that split second.

“I, Xiao Se, ride only the finest horse and wear only the richest threads! This fur coat of mine was specially sewn by some of the finest seamstresses in the imperial capital in the August Threads. Just sewing it took three whole months, shipping it, another one. Hmph, a hundred silvers? That’s not even enough to buy the sleeves of my coat!”