Mechanics & Inner Workings
It is in part soul magic. By soaking the stone in the blood of a victim, a piece of their soul is trapped within the stone. It can only be released once a bit of soul from the perpetrator is absorbed by the stone. However not many people understand this about the bloodstone and just generally get a bad vibe from them.
"There is no place for bloodstones in our future as a people." --Anika BluehairBefore the Accords unified the Numabian tribes, feuds were common between them. Bloodstones serve as a marker of a life debt owed, usually vengeance for the death of a loved one. The stone is soaked in their spilled blood or ashes and then hung as pendant on a chain or leather strap. The wearer must then actively search for vengeance and can only be relieved of their duty once they "sate" the stone in the blood of wrongdoer. This used to be a common practice for settling disputes and feuds within the Wastes and Borderlands. The practice fell out of favor when Anika Bluehair, who had worn a bloodstone for the death of her tribe, took off her stone unsated and left it behind in the sands. By relinquishing her stone and urging others to do so as well, she helped to end this feuding practice, though it took a while to fully die out. There are still some traditionalists who use them today, but it is extremely rare and saved for only the most severe of crimes/retaliations.
When a person begins a blood stone, they are not supposed to take it off. If they take it off before the stone is sated, then the spirit of the person the blood stone is for will go un-avenged, leaving a restless spirit to wander the Wastes looking for someone to complete the vengeance cycle. A blood stone is supposed to strengthen the wearer in their pursuit for vengeance. Not necessarily through an increase in strength but by increasing the commitment to avenge them in whatever means necessary. They are now seen as bad luck, with a restless spirit attached to them that will curse the unsuspecting person who comes across them, as they will always be thirsty for blood. People who wear them and continue the practice are seen as barbaric, dangerous, and unstable. It is not a good thing to find out someone is wearing a bloodstone. Because of their sordid history, there are a few morbid collectors in the Borderlands (Deefin Gate) and Piromere who will pay lots of money for anyone brave enough to find bloodstones and bring them back to the collector. There are stories of those too reckless or stupid to ignore these tempting offers and are later consumed completely by an unsated bloodstone they found or are corrupted in the process and become meaner and more violent.