MTL - God-level Bodyguard in The City - ~ nameless

That night, she shed off the image of a young maiden’s immaturity, forming a ripple in the deepest parts of the Cold Palace…

That day, she kneeled before him begging for mercy. She didn’t want anything. She only wanted to leave the palace and become an ordinary girl….

A bunch of elegant and good looking heavenly princes. A lowly palace maid with a mind as calm as still water.

If they were to meet, would it be an encounter like dewdrops and the autumn wind or would it be a lament of a country…

- Description from Novelupdates

When an S-class elite assassin-raised captain of a special ops suicide squad comes home from a high-stakes Africa mission, he finds himself offered something that could potentially set him up for life- a curious assignment that he could use to finally exit his days of war and slaughter.

The world experienced a cataclysmic change, and countless spatial gateways appeared out of thin air.

Exotic beasts of all shapes and sizes swarmed out of those aforementioned spatial gateways, forcing the humans to face the crucial moment for their survival.

In order to search for a chance at survival, brave warriors from the army and scientific researchers risked their lives and entered the world beyond the spatial gateways. To their surprise, they discovered that there was a chance of obtaining beast cards by killing these exotic beasts in their world.

Those with extraordinary spiritual strength are able to utilize the beast cards, perhaps transforming the cards into the beasts’ combat bodies while they were still alive, or transforming them into weapons or defensive gears, or…

A new occupation came into existence following the changes, known as beastmasters.

A transcender with two souls fused into one found himself in this magnificent new world full of waves, rising step by step as he ascends into the seat of a godly beastmaster.

- Description from Novelupdates

This stands at the forefront of strategy guides to Life (a shitty video game)!