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.
