HxH : Pokemon Master - Chapter 20: Menchi Request

He rose from hardship, but was felled by betrayal. From then on, one man, one gun; treads the path between Evernight and Daybreak to became a legend. No matter what was destined to be his fate, he intends to become the ruler who dictates.

The strongest King of Soldiers returns to the city of flowers, becoming his fiancée's cohabiting bodyguard!

The celestial celestial beings who lived for more than 100,000 years were born and reborn in a small monk in a human world.
His motto: “It’s not as good as a medicinal medicine for ten years of hard work.” “Even if you practice a copper-iron bone, it’s not enough for my soldier’s attack.”

- Description from Novelupdates

Worlds overlapped, and Alien Species descended.Strange entities emerged one after another, as the shadow of evil spread wildly.The calm of life was shattered, and Zhang Xiaoman, inside a fish's stomach, accidentally consumed a system named “World-saving Plan”.From then on, he became the only person among all humans with Extraordinary Power.…Inventing an ancient oath, he established a unique methodology, Cultivated Dark Energy, founded an organization, took Control of the Transcendent, and resisted invasions.Well, this is actually the story of how a Big Con Man bluffed his way into saving the entire world.PS: Contains elements of the behind-the-scenes, Cthulhu mythos.