The Crystals concept in Final Fantasy has always been about balance. However, players only get to see the side of the story for the perspective of the Warriors of Light. The Warriors of Dark and the Dark Crystals are NEVER evil. Many times, in the past, civilizations tried to over utilize "light" and the Warriors of Dark were called in two reset the balance; so in Final Fantasy, light can overstep it's bounds too. It's like Yin-Yang... If Darkness begins to take advantage, Warriors of Light are created to push the Darkness Back. If Light begins to take advantage, Warriors of Dark are created to push darkness back. Zodiark may be the Dark Crystal.