A Link In the Chain of Sin

Only kill the killers...

The creature looked down at her, smiling ear to ear. She screamed, and it flinched at the sound. She raised an eyebrow as it stumbled backward and nearly fell. It regained balance, and gave her a smile. The grin glistened as it showed the entity's sharpened teeth. It spoke with a whistleing lisp and she found it oddly endearing.
"My name is chorusine," it said, its arms flying out in a wide and welcoming gesture. It leaned in and gave her the most comforting hug. "I will certainly betray you and consume the whispers of your death. It's so nice to meet you."

Simply called "Chains of sin" are a form of eldritch entity summoned by The Scholars of Sin. The cult uses these entities to hunt their enemies, but it always comes with a risk. The chains are intelligent, predatory, and nearly unstoppable. It's inevitable that they will betray the one who summoned them, no matter how friendly they seem at first.
The chains of sin are hunters to a fault. Point them to a target and they will hunt it endlessly until finally making the kill. This is because their lives are dependent on the kill, as the only thing they can feed on is the last breath of victim they kill. Without it they will die and fade Into oblvion. Every one of these entities used to be a member of the cult, ascended through means unknown to all those not of the highest rank in the organization.
That remember adds to the chain, and every member must remember how that chain binds us all. For every kill you demand of the creeper it will keep a tally. They will keep tabs on how righteous these kills are. It may be tempting to eliminate your enemies for past slights, but even the creature would caution against it. For In almost every religion, murder is a sin.

The Chains We Carry

Every member of the called has their own Link in the chain, both literally and figuratively. Each member commands their own entity. These entities act like mentors in many ways, easing in the cultist's understanding of the universe and slowly increasing their Candlelight.
Overtime, the cultist will need to feed the creature with the dying breath of a kill by the entities own hands. You'd be surprised at how few enemies one persin can have. While at the beginning, the cultist may boast a long list of potential recipients of Justice, the excuses they have to justify the kill become increasingly flimsy. Eventually, they will struggle to find someone who has done wrong.
They need to search for the worst humanity has to offer, and through the enactment of justice, the creature will be satiated for another cycle. The creature will be hungry again, however. It is never ending. The creature will, given enough time, catch the cultist without a suitable kill.

Penance

Should the cultists be unable to provide a kill, their lives are forfeit. This is the nature of their contract. there are ways of postponing this inevitable outcome. Their god is harsh, brooding, and cold, but not without understanding. A cultists may need to offer up an innocent to save themselves. This is a sin, the greatest sin, and if they wish to keep their life, they must repent.
The Scholars of Sin routinely enhance in flaggelation as penance for unclean deaths. This is not a permanent solution. Eventually, the cultists start to resentment the pain. They won't feel as bad as they should, and that's when the entity turns on them.
The entity will consume them, transform them into something like itself. They serve Their god for eternity, a living embodiment of their failures. They ascend, but they do so in disgrace. Despite their warnings, their ranks will grow. Such is the cycle of sin.

Appearence and Behavior

Chains of Sin are human in appearance, but their skin is flayed, strips of flesh hanging from the muscle and bone. They have black eyes, sharp teeth, and their arms and legs are much longer than normal. They are quick and tireless, especially when hungry. Even if exorcised from reality, they will harbor a brute against the one who removes them. Should they be summoned again, their first order of business will be to find the one who cast them out, or a close relative if the culprit is dead.
The Chains of Sin are raw, emotional beings. They wear their heart on their sleeves. They are extremely polite, and sensitive if others are not. They are not inherently violent, however, more likely to cry than attack. If a quarry escapes them, they will often sulk, brooding for hours before continuing their hunt. They befriend the cultist who summons them, and it hurts for years when they inevitably have to kill them.
They warn their friends, constantly. They do everything they can to urge the cultists to be as tireless as they are. Sin is in no short supply. No one ever succeeds. It comes as no surprise that they have little hope for humanity, but nothing will keep them from giving another chance.