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.
The very last measure a fighter could take to win a battle was to burn his own soul. This almost always resulted in death, as it took many special artifacts or a huge amount of energy to restore the damaged soul, which could be compared to how much was burned.
The energy in the souls was special because it was a concentration of all the energy a person absorbed before, so even to restore 1% of a soul, it could take several legendary souls or literally millions of ordinary souls and they had to be used as quickly as possible to avoid death.
It was a desperate move since fighters decided to burn their souls only in desperate situations, so it didn't help most of them anyway, however, sometimes it could not only save a life but also help them become stronger after a very hard test.
Tremble. Tremble. Tremble.