An Extra's Rise in an Eroge - Chapter 12: System

Thousands of years ago, a small planet collided with Earth and destroyed the world. In five days, ninety percent of humans had been wiped out, leaving behind the last ten percent to earnestly struggle on death’s door.

Jinyu was one of those people who survived. Due to a special heredity trait, he could understand beast language. After the apocalyptic disasters, Jinyu had been living for a month with the few small beast brothers that he’d subdued. Previously, Jinyu had thought that he would live like that until he died. Yet, inexplicably, one day he opened his eyes to find that he was in a monstrous, lawless world that was full of vitality and life.

Jinyu’s transmigration into the future let him skip over almost one hundred thousand years. In the year 106825, beasts rule the galaxies and ‘pure’ humans are extinct. As the one and only ‘pure’ human left in the entire universe, Jinyu braves this new chaotic world to find a place for himself and thus begins to work at Beast Store number 138.

- Description from Novelupdates

What is my 1000-year-old monster self to do when I’ve failed my immortal ascension? Time travel — accidentally — and wind up back in my 9-year-old body, needing to re-cultivate, of course. But after that? Get REVENGE! Muahahahaha! But the idiot who killed me — also accidentally — was the main character of the dumb harem Xianxia I transmigrated into. But wait. Wasn’t he only 7 or 8 at this point in time? Well, since I can’t harm a child or the main character without suffering in some way, then I’ll just have to raise him better, faster, stronger, and loyal! Muahahahaha!

With the revival of spiritual energy and the breakdown of the order of species, it is a difficult test whether human beings can still stand at the top of the biological chain.

(There is already an old book, The Strongest Descends in the City, you can read it.)

- Description from novelbuddy