To be honest i think the crystals are gana be used to a) make some amazing weapons or b) kill a boss or c) unlock a portal. Now these 4 crystals have something in them that lets them fly and have these abbilities. I dont really know what it is but i do know one thing. If you take the Fear Crystal thats in the house where you found it there should be a devil or monster. Now if you get close to him holding the Fear crystal he will dissapear. Now i dont know what this could mean. Maybe hes the boss or maybe an enemy that you will fight. That is if the develepors give you the ebilty to use weapons and attack other enemies. I dont know what exactly the Develepor is going to do but i know that theres gana be something with this Fear Crystal and that maybe it has something to do with the Protection Crystal.