Note: Also called Soul Chain.
Soul Shackles are used by the Dark Guild to prevent betrayal. In the event of anyone being captured, they can just activate the Soul Shackles to kill them. In order to activate them a corresponding seal stone needs only to be crushed.
After the attack by the Abyss Demon, three black gold rank demon spiritualists were captured. However they died before being questioned because of their soul shackles.