Blacksmith Vincenz:
Now, I'll tell you about Soul Crystals. Originally, Soul Crystals give a special ability to weapon by using the spirit of monster. Especially, in the past, you had to have a Soul Crystal when defeating monsters to raise the level of the Soul Crystal. This wasn't an easy task but, those who desired to become stronger spared no effort.
But at some point, it became impossible to experience the Soul Crystal that way. Well... there are lots of strange things taking place nowadays, so stuff like this is not unthinkable.