Grims

"All Supernatural creatures are monsters but Grims, they are the worst breed of monsters."

- Ex-Church official Grim also known as Sins of Natures or Beasts of Sins is a term used to describe supernatural creatures who after consuming massive amount of blood of other supernatural creatures become sociopathic and lose their personalities. Grims are similar to stray devils but immensely stronger, and unlike stray devils which is a class specifically for reincarnated devils, Grims can affect any living creature except angels (due to them being bound by God's system). Grims are shown to be one of the worse and oldest enemies of Grim Reapers thus being the origin for their names, with the original Grims rooting from evil spirits.

Several factions including Hades, Norse, Greek, Angels, Devils, and Fallen Angels have all created special anti-Grim households in order to exterminate and prevent the growth of grims. Odin has even revealed that as groups like the Khaos Brigade grow more prominent he fears the Grims that could come from these groups.

An immortal by the name of Niklaus is shown to have created an entire group made up of Grims, even turning these Grims into hybrids through the use of his own curse.

History
During the Great War, there existed a group of creatures who survived by consuming human blood and creatures who lived by consuming human bodies. These were known as vampires and ghouls. Grims on the other hands, were creatures from any race who thrived off of consuming the blood of other supernatural creatures or their flesh. When a supernatural creature consumes the blood it can activate unimaginable powers, such as Gasper when he consumed the blood of Issei and used his powers to defeat the female magicians. However, creatures who consume the blood for long terms develop an unnatural addiction. These creatures thus become known as Grims.

The first grims were typically Evil Spirits who would consume the blood of devils and other creatures, obtaining a portion of their demonic power in the process. These evil spirits were the first known Grims who would tie themselves to the physical world. Due to being viewed as a disgrace to nature they were obviously hunted down by Hades and his reapers. After a while Reapers became known as Grim Reapers due to their hunting of Grims.

But soon there came to exist an even stronger and darker groups of Grims. During the Great War, unable to cope with war and their abandonment by their Lord, fallen angels began to consume the blood of devils and other angels, some even going as far as to consume their flesh. These fallen angels began to go through monstrous transformations, gaining fangs like vampires, claws like werewolves, and dark yellow eyes. Azazel however saw nothing wrong with it until he learned of the personality changes. These new grims became sociopathic, predatory. They become like beasts, seeking only pleasure and enjoying causing harm and mayhem wherever they go. The Vampire Queen even goes as far to state they have "lost all their humanity".

It was later revealed that among the old satan faction, there existed devils who have undergone this transformation by consuming the blood of devils from the New Satan Faction. This practice was then revealed to have spread throughout other creatures in the supernatural world, however it was then banned by numerous factions who viewed it as a "damnation of nature", even going so far as to be punishable by death.

Summary
Grims are shown to be extremely predatory in nature, sociopathic, seeking only to cause harm to others and to feed their addiction for the blood of supernatural creatures. Most Grims are revealed to enjoy the blood of the creature they formerly were, with devil Grims for example enjoying mainly the blood of devils. The most extreme cases however, are shown to consume the flesh of other supernatural creatures and these Grims are revealed to be the strongest of Grims. They are shown to not care about their own families and friends with their old relationships mainly ending in destruction. Grims are shown to enjoy hunting and terrorizing humans, even going as far as to treat them as nothing more than meat, most Grims thus become like vampires drinking the blood of humans and consuming their flesh, however when a Grim conduct such behavior they do it in a more, bloody and destructive type of way, uncaring about being seen or discovered by average humans.

The way Grims are shown to not care about exposing the supernatural is revealed to be what makes them one of the Greatest threats to most factions. As even one Grim threatens to expose them all which can lead to their own destruction.

Despite their nature and reputation, some Grims are also capable of human emotions, such as compassion, love, protection, respect, and self-control. Not all Grims are evil killers with no conscience, there are some who are just tragically consumed by their bloodlust to the point that their morality is irrelevant. It is revealed that after feeding or massacres there are even grims who will feel remorse and cry over what they did, such as the case of the famous Ripper, a grim from England who feels remorse after killing and thus tries to put the bodies back together

By consuming the blood of supernatural creatures, Grims are shown to go throw horrific or even disturbing transformations. This is shown numerous times, by grims growing fangs, eyes, limbs, nails, and even a unnatural third wing, or even their ears and facial features transforming to accommodate the newfound energy mutating inside their bodies. There is a way to cure a grim, however it is different depending on the species that the grim formerly were. However because of the work it requires and how difficult is can be, especially when fighting with a Grim, they choose not to instead seeing it better as to simply kill them.

Abilities
When Grims consume the blood or bodies of other supernatural creatures, they gain a portion of their energy. This causes them to gain a immense amount of speed, strength, durability, and even a portion of their energy and power. Grims also gain numerous number of extra fangs, claws, and other assets that can aid them in battle, however a major drawback is that most Grims tend to go insane when using these things making it impossible for them to think in the middle of battle.

Due to the death of the biblical God, Grims are shown to have no limit to the different powers they can gain from other creatures with fallen angel Grims gaining the ability to manipulate and wield demonic energy, to even devils gaining the ability to manipulate and wield light energy. This is the reason Grims are viewed as so dangerous and monstrous, as their abilities is a very contradiction to nature and combined with their sociopathy and insanity they become dangerous enemies.

Known Grims

 * Kali Bael also known as The Ripper of England, a widely known and famous Grim. One of the first Grims to make an appearance among devils. He is over two centuries years old and is still active to this day. Despite being sociopathic however, he has still managed to keep his sanity causing him to become very cold and calculating. He is shown to consume the blood of mainly fallen angels and humans however it is revealed he will also consume devils and demons when given the chance. He gained his nickname due to his terrorization of England in the 1500s.
 * Camiel, another famous Grim who was once a member of the Grigori during the Great War. After consuming the blood of multiple devils and vampires she then left the grigori after the persecution from Azazel and other fallen angels who realized the threat she posed.