Forbidden Materia

[Holyomen]

This "Dark Side" of materia crafting is said to be the most powerful, but will come at a cost.

So what will the cost be?
What are we able to sacrifice?
Gil? Time? Gear? Anima? Guardian's Aspect?
Perhaps none of those but it may be a different kind of sacrifice.

When they use terms like "Dark" or "Forbidden" to describe this materia enhanced gear it brings to mind Cursed Armor. Armor or weapons with a soul of their own, that uses the possessor as a host to carry out it's dark wishes.

So it may be that this Dark Materia Gear may take your body in some way.
It could possibly:
Slowly drain your HP or MP
Increase your enmity
Have a very low durability

Or my personal favorite, the price of wearing this evil gear is your body itself.
Once crafted you will not be able to remove the armor from your body.
In a game designed for variability, you pay the ultimate price of having no choice.
So not only can you not change your gear, but you will also not be able to change your class.

That is, until you pay for the "evil" materia to be "purged" from you.