Eroge: I can Travel To The Ancient World - Chapter 16: Marriage And Trouble

As part of the imperial family, every move by Chu Yuan in this game of chess is made with apprehension, fearing that with a moment of inattentiveness, the whole match will be lost in a single move. Ascending to the throne at eighteen, not half a year passes before civil strife erupts in Yun Nan. Though the thoughts of the old guard at the imperial court are not exactly identical, they are all waiting to see how the new emperor will put an end to this. Unexpectedly, before this side could make a move, a few thousand miles away, the King of Xi Nan, Duan Bai Yue, had already personally commanded troops to attack in all directions; not half a year had passed when peace was restored. Sparse moonlight shines into the palace; Chu Yuan stamped the wax seal himself, and had a secret letter sent urgently to Yun Nan 800 miles away — this time, what must we(1) give in exchange? Brush marks passed through the back of the paper; it almost can be seen, when writing this line, how angry the young emperor was. Duan Bai Yue spread out a piece of paper unhurriedly, replying with only one word. You.

He rose from abjection and achieved eternity in glory.
He embraced the prettiest beauties and killed the strongest opponents.
He was able to shift the clouds into rain and cover the sky with one hand.
He could overrun the entire world and go anywhere as he pleased.
He pacified wars and held the world in awe.
He was matchless in the world.
However, his hair turned white overnight for his beloved woman and he was on the verge of death.
He was surrounded by enemies who were trying to take his life.
He struggled his way to become mighty and fought for everything he cherished.
For this age, he was the only king of the Dark World.
His name was a byword for might.
As a man living in the world, his only ideal was to pursue brilliance.

- Description from Novelupdates

Nyx, Earth's former number one mercenary found himself on the end of his life failing to escape from a powerful criminal mastermind. However, fate seems to have another plan for him when he woke up in a completely different place, a place that he will eventually call home in the new world where strength makes one the biggest boss.[Welcome to the Universal Shop System!][Detected that it is the first-time log-in. Reward: Random Gift Pack (5)][Detected the user entering the Body Tempering Realm. Reward: Infinite Qi System][Opened Random Gift Pack (5). Acquired True Transcendence Body Art (1). Acquired Primordial Nihility Transcendent Qi (1). Acquired Immortal Illusion Art (1). Acquired Grand Desolation Transcendent Body (1). Acquired Extreme Origin Transcendent Soul (1)]With an absurd system as his cheat, follow the young man's journey through the entirety as he gains his position as the one true peerless existence, the sole transcendent above all.

The invincible strongman who roams through the city by day and night, a supreme soldier king that moves across the urban landscape.