Fully implemented discrete demon will, which means the demon crystals can be inserted into demon crucibles to create will.

src/main/java/WayofTime/bloodmagic/api/Constants.java

@@ -160,6 +160,7 @@ public class Constants
         BOUND_SWORD("ItemBoundSword"),
         BUCKET_ESSENCE("ItemBucketEssence"),
         COMPONENT("ItemComponent"),
+        DEMON_CRYSTAL("ItemDemonCrystal"),
         DAGGER_OF_SACRIFICE("ItemDaggerOfSacrifice"),
         INSCRIPTION_TOOL("ItemInscriptionTool"),
         LAVA_CRYSTAL("ItemLavaCrystal"),

src/main/java/WayofTime/bloodmagic/api/soul/IDiscreteDemonWill.java

@@ -0,0 +1,29 @@
+package WayofTime.bloodmagic.api.soul;
+
+import net.minecraft.item.ItemStack;
+
+public interface IDiscreteDemonWill
+{
+    public double getWill(ItemStack soulStack);
+
+    /**
+     * Drains the demonic will from the willStack. If all of the will is
+     * drained, the willStack will be removed. Will only drain in discrete
+     * amounts, determined by getDiscretization.
+     * 
+     * @param willStack
+     * @param drainAmount
+     * @return The amount of will drained.
+     */
+    public double drainWill(ItemStack willStack, double drainAmount);
+
+    /**
+     * Gets the discrete number for this demonic will.
+     * 
+     * @param willStack
+     * @return
+     */
+    public double getDiscretization(ItemStack willStack);
+
+    public EnumDemonWillType getType(ItemStack willStack);
+}