Unscientific Beast Taming - Chapter 66 - Battle Power Unit

Setsuna Shū is a magical girl with temporal magic that allows her to go back to the past whenever she performs a certain action. She works as a magical girl, hunting monsters and helping people… or at least, that’s what she lets everyone believe. In truth, she made a contract with a demon so she could return to the past and rewrite the future.Her real reason for turning back time is to save her “sister.” As a child, she had no parents, relatives, or friends. When she was finally adopted, her sister became her entire world — and for her sake, Setsuna wouldn’t hesitate to sacrifice the world itself. She gave up her original gender, her past “existence,” and even parts of her freedom in a demonic contract, all for the sake of saving her sister and taking revenge on the monsters that hurt her.But… is that really all there is to it? Or is Setsuna, in the end, partially responsible for everything that happened?

I lived for you in the last lifetime, everything I did was for you, yet you wanted me to die; so, this time, life is mine to live! This world lied to me, betrayed me, and humiliated me, and I am back to change everything!

- Description from Novelupdates

Once all people received Souls and incredible powers. Some were lucky enough to obtain the Soul of an ancient and powerful creature, but fate was not favorable to all.

The world began to change, and creatures evolved. But, it was not the beginning of a new era. It was the end. A couple of months later, a dark mist appeared and destroyed the world. It was a dictate of destiny from which no one could escape.

Wain Norheim was the world's best assassin and the only one who didn't get a soul. However, he was destined to gain the power to confront fate.

Escaping through a portal into another world, he unknowingly began the apocalypse. Even the world failed to expel him.