This Japanese Monogatari Isn't Lame - Chapter 49. Encounter

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

When I cleared the final chapter of a game that was a national failure, I became an unnamed side character in it.

A non-standard, unmeasurable, EX rank supporting character.

Mimizuku, a small girl with chains on her wrists and ankles and the numbers “332” branded onto her forehead, wanders into the Forest of Night seeking to be eaten by a monster. However, when the ruler of the monsters, the mysterious and beautiful “King of Night,” refuses to eat her, she tries to formulate a way to convince him otherwise.