Kyoukai Senjou no Horizon - Volume 2B, Chapter 32: Man and Woman in the Plaza

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.

Carlos Valois thought dying once was enough—until he woke up as a 10-year-old in the world of “The Dark Era,” a game he'd mastered in his previous life.Born as the last heir of a fallen noble house, Carlos discovers he's destined for a tragic fate: in six years, he'll be manipulated into joining the dark forces and killed by his own childhood friend. But this time, he has the ultimate cheat code—memories of the future.While other kids play with toys, Carlos hunts for divine legacies. Using his game knowledge, he performs an ancient ritual and steals a Demigod Mark from the thousand-year Sacred Oak—a power that should have remained hidden for decades.At 15, Carlos awakens as a Death Herald with broken stats that shouldn't be possible. Most Death Heralds are fragile summoners hiding behind weak skeletons. But Carlos combines his necromancy with stolen divine abilities, creating a hybrid build that turns him into an unstoppable force......[Skeleton Warrior has successfully evolved into Purple Thornblade Skeleton Guard!][Purple Thornblade Skeleton Guard has activated Bond: Glory of the Purple Thornblades!][Twelve Purple Thornblade Guards have formed an Undead Armored Knight Legion!].....His skeleton warriors aren't cannon fodder—they're elite undead legions enhanced beyond normal limits through secret evolution paths that took thousands of players years to discover.Every “coincidental” encounter is actually Carlos farming legendary opportunities. While his sister thinks he's just a lucky genius, Carlos systematically raids every hidden treasure, secret technique, and forgotten legacy he remembers from the game. Ancient bloodlines, divine artifacts, mystical cultivation methods—if it exists, he's taking it.With his infinitely evolving undead legion, Carlos set out on a path to rewrite destiny and become the supreme Death Herald legend.

What would you do if your entire world were turned on its head? A Primordial System buzzing in everyone’s heads, displaying strange screens and other displays in their visions. Being thrown into a tutorial before entering your first System Event broadcast across the universe. Returning back to your home after the System Event to realize that it’s been filled with Gates leading to monster-filled domains, a good number of which have already broken and released their monsters into the world. And learning that the abilities every human being has – abilities that have led to the current structure of society – are nothing but the root of their Skill Trees. The very first skill in their Skill Tree out of many. Well, Ashley doesn’t know. She doesn’t remember anything other than some basic common knowledge from before waking up at the start of the tutorial with amnesia. So why should this change anything for her? Other than her finding out about the blood bestowed upon her by a certain primordial and her own Skill Tree. One with just a single skill. A skill to unlock the skill trees of those she kills. To assimilate. What to expect: Skill Trees, LitRPG Apocalypse, Skill Tree Assimilator(the ability to take the skill trees of those the MC kills that she can unlock through Skill Points without getting the skills right away), Livestreamed Dungeons, Livestreamed Public Battles and Events, Chaos Magic, Varied Magic due to Skill Tree Assimilator, and the MC does not start off strong in the start and only grows strong as she assimilates more skills from those she kills, the MC starts out without any memories and few emotions and slowly gains them throughout the series. What not to expect: I do not write romance(for the main protagonist), there will be no harem, there will be no reverse harem, and do not expect a really strong MC at the start of the story as she has to grow into that role.

“Stripped of his power, betrayed by those he trusted, and abandoned by fate itself, the young master of the Celestial Clan faces a choice: cling to the tattered remnants of his righteous path or to embrace the darkness blooming within. When a catastrophic fall strips him of everything, he, along with his fiancée by his side, abandons the righteous path. Witness the birth of an anti-protagonist couple, as they forge contracts with ancient, terrifying beasts and carve a new destiny from the bones of their enemies.”In the heart of the Azure Star Continent lies the legendary Celestial Clan, rulers of an unbroken legacy of power, wealth, and influence. At its helm stands Xian Tianyang, a prodigy born with unparalleled talent and destined to inherit the mantle of leadership. Calm, calculating, and relentless, Tianyang has forged a reputation as an unshakable force, a young master whose genius is rivaled only by his ambition.But the path to supremacy is fraught with danger. In a continent where alliances shift like desert sands and rival factions sharpen their blades, Tianyang must navigate a world of intrigue and betrayal. When his childhood fiancée, Lin Yuqing, the “Blooming Empress” of the Eternal Bloom Clan, enters his life, their union threatens to spark both alliances and rivalries that could reshape the continent.With ancient secrets lurking in the shadows, enemies plotting from every corner, and the weight of his family’s legacy on his shoulders, Tianyang must prove that he is more than just a prodigy—he is the heir to the Celestial Throne.Will their fates intertwine as destined rulers, or will the fires of ambition and duty tear them apart? Prepare for a tale of genius, power, and forbidden emotions, where every choice has the power to change the fate of nations.