One Piece: Supreme Check-In System - Chapter 22: Vash the Stampede vs. Kizaru – The Gunslinger’s Dance with Light

In a game-like world where dungeons, monsters, and players appear.

In a monstrous post-apocalyptic setting, this is a story of how a lowly Inventor, Lance, conquered a nation governed by immoral group of Scientists called The Corporation. He grew and climbed up to the highest rank possible as a Scientist with his inventions and side businesses. Eventually, he became a weapons inventor, building weapons to two opposing sides. In doing so, Lance always crossed a dilemma. How could a nobody topple the most powerful government? How could one overcome circumstances beyond his grasp, especially in a world filled with monstrous mutations called the Abominants?

It was a time where demons roamed the earth and chaos reigned. The story took place in Luoyang, the legendary capital of the times. During the night, one could find people holding on to their food with dear lives as they faced off against stray dogs, people with weapons in hand vowing to fight against Fate to their very last breath. There was bloodshed everywhere as some died meaningless deaths, while the strong tyrannized the weak and the truth was frequently hidden. Some of the citizens had completely lost their mind, while some died on their travels. Most importantly, the words of a certain youth caused much panic in the human world. It was a time of little warmth as nights in the capital were frequently accompanied by gusts of wind and rain, and it would be covered with snow during winter. Such were the days…

- Description from Novelupdates

This legend tells the tale of the protagonist, Kuroki summoned to protect the demon king from the hero.

Kuroki, unbeknownst to him, suddenly came to another world. He was summoned by the demon king, Modes. The territory which the demon king overrules was in the midst of being destroyed because of the hero. He had no choice but to bow before Kuroki.

“Please save us, Savior Dono!”

Kuroki nodded, deciding to save the demon king due to an unexpected turn of event.