I imagined that the "witch" (I use that term loosely, she is never referred to as a witch until she goes against the family's wishes) pulled together what parts of a soul were in the womb, and bound them together with Talia and Amond's affections. Over time this binding fused together the soul into a mostly viable person, but when the spell was broken there were large gaps left. Holes cause a combination of emotional and physical pain where an aspect of her (such as her capacity for empathy) once was while the parts there are (such as anger) attempt to fill what is missing. It's similar to those who feel pain in phantom limbs, which is caused by the brain overtaking the parts used to control the missing limb and applying them to different tasks.
These holes are not a terribly uncommon occurrence in people but the holes most have are small and get repaired with time or stoppered with something such as drugs or a new puppy. Unrepaired souls make a fabulous foothold for evil influences which is why there is usually some trauma associated with those who walk that path. What makes that route doubly tempting is that when someone is killed their soul momentarily passes through that of the killer and fills in those gaps for a few seconds. Beating a person within inches of their life brings them within touching distance and has a similar though less dramatic effect, as does intimate sex (though the conditions for that are difficult to meet as it requires nothing short of true love).
In effect, Snap's soul is filled with many large gaps and cracks making it a breeding ground for the essence of the nether realms. She's caught between the person she knew she was, and the person she feels she is. The monks taught her to manage the constant pain, the consuming rage, and the breeding evil, but none of it ever goes away. If she ever lets her guard down at least one of these will overtake her, and no one is sure what happens after that.
The blackened and withered Hand of Callous Justice is forever trapped in the shape of a fist. Shrunken with age, someone long ago had the idea to incorporate it into a necklace so that the emblem of unflinching loyalty to the law could be worn about the neck.
Those wearing the Hand of Callous justice feel themselves strongly compelled to enforce the law in the harshest way possible- all but the most minor of violations demand the death of the perpetrator. The Hand's demands must be met immediately, lest the owner be stricken with unbearable agony until justice is served.
The Hand allows its owner to immediately become aware of any crime or dishonesty done in their presence, immediately granting complete immunity to the Criminal's attacks. Those using the Hand of Callous Justice find that those they are hunting are completely unable to strike them, their attacks passing through the hunter harmlessly.
The Hand carries a great burden of responsibility- should its owner commit a crime, the Hand of Callous Justice will demand their death, and subject them to relentless suffering and pain until their death- whether at their own hand, or by the next owner of the Hand of Callous Justice.
This is an exquisite item, and a very original weapon. However, I feel that the item itself could use a little more description, and the backstory as written is really confusing. Who is Gen? Who is the lady that Devorak falls in love with during exile? And what did Hestor mean to him anyway? The dialog is good, but there is just not enough context given to allow comprehension of the major events. I love this item, but will withold my vote for awhile to give you the chance to clear up or remove the backstory.