Grimm (RWBY)

The Grimm are the primary monsters of the world of RWBY, which inhabit various parts of Remnant.

They are described as "creatures of destruction" and lack a soul; hence, they are unable to use Aura. They are in turn also drawn to feelings of negativity such as envy, sadness, loneliness, and hatred and will often congregate towards the source of these emotions.

At one point, ancient cultures believed that Grimm were animals possessed by evil spirits, or were the spirits of once tortured animals.

History
The Grimm are said to have appeared soon after the dawn of mankind. They have targeted early Humans for as long as can be remembered, seeking to destroy them and all of their creations. At first, it seemed as though they would succeed as Humans did not have the strength to fight them. However, Humans discovered the power of Dust and with it, the Grimm were driven back. During this time, Humans enjoyed a time of peace and soon formed their own kingdoms, which grew to survive and prosper. This time will not last forever, however.

While Grimm are initially mindless and heedless of risk during their youths, to where they will simply attack any humans on sight, some Grimm are so powerful that they have survived to live for hundreds of years, and in that time they have evolved and learned from their experiences fighting humanity. In doing so, they have exhibited restraint and the patience to avoid taking unnecessary causalities in futile conflicts. Instead, they stay close to humanity's borders, waiting for the opportunity to come where they can finally strike, and thus mankind is always in ever present danger, even in times of apparent peace. This was stated by Dr. Oobleck in the episode Search and Destroy, when he tells Ruby on how intelligent some species, such as the Goliaths, have become over the years.

Additionally, the Grimm appear to be the predominant species in the world of Remnant as humans and Faunus appear to be limited to four primary pocket settlements referred to as Kingdoms, which are guarded by Hunters, as well as several villages with mixed success. Attempts by the Kingdoms to expand beyond their borders are often met with resistance, and even failure, as the loss of an entire sector of the city of Vale overrun by the Grimm can attest to.

Biology
The origins of the Creatures of Grimm are unknown. Ancient human cultures believed the Grimm were animals possessed by evil spirits, or even the tortured spirits of animals themselves. Further study has disproved this theory over time however, due in part to the discovery of even more horrific misshapen species of Grimm which have no animal counterparts. With the discovery of new types of Grimm every day, scientists are left with more questions then answers.

Grimm come in a variety of shapes and sizes; the latter appears to be a factor of age, and are said to be the only creatures without souls, thus being deprived of the use of Aura, but making up for this with strength and savagery. Grimm are stated to be attracted to generally negative feelings such as sadness, hostility, anger, fear, etc. and even congregate to areas that, although humanity has long since abandoned, still hold residual traces of these feelings.

This behavior will even lead to them to join in on an attack in progress if the humans being attacked begin to panic. Grimm typically form packs or other types of large groupings with other members of their own specific species. While some lone Grimm may stray from the pack for hours or even months, they will inevitably rejoin their group to continue their instinctive drive to hunt the people of Remnant and destroy any artificial creations associated with them.

The longer a Grimm lives, the larger it becomes, with species such as the Nevermore ranging from the size of an average bird of prey to massive pterosaur-sized beasts after hundreds of years. This added size comes with an ability to learn from their encounters in contrast to the Grimm's more reckless nature during their youth. While sometimes requiring hundreds of years, the Grimm's accumulated experiences over the course of surviving their battles with man can cause them to begin exercising caution.

This perverse form of self-preservation can even lead them to avoiding unnecessary conflicts altogether. Yet, despite this ability to learn, their instinctual hostility still remains, as shown by their preference to patrol the borders of Kingdoms for any weaknesses they might someday exploit. This demonstrates that for all their apparent intelligence, older Grimm simply use it as a means to become more effective in their singular drive and purpose, to kill.

Grimm display no enmity towards normal animals, and they only clash during territorial disputes. Humans and Faunus are the only races they attack on sight. Grimm can also choose not to display feeding behavior and it is commonly believed that they do not require sustenance. When Grimm die, their corporeal form evaporates, preventing detailed anatomical or biological studies. Huntsmen that kill for sport cannot stuff and mount Grimm bodies as trophies (making do with replicas instead).

Also of interesting note is that Grimm usually die off when in captivity (if they cannot kill their captors or escape first), implying that they cannot be kept alive by normal means. If the theory of Grimm not needing to feed is true, it is entirely possible that they survive on negative emotions or the act of killing itself.

Volume 1
As part of Beacon Academy's initiation, new students must team up in the Emerald Forest and fight their way to a temple, encountering several different types of Grimm in the process. Ruby Rose and Weiss Schnee are attacked by a large pack of Beowolves, but are forced to flee when Weiss' attack causes a fire due to Ruby's accidental interruption.

Yang Xiao Long is also attacked, but by two Ursai that only manage to sever a strand of her hair, sending her into a blind rage as she defeats one of the Ursa, as the other is killed in one strike by Blake Belladonna before Yang can finish it off. Likewise, Lie Ren is attacked by a King Taijitu, which he defeated through the use of his Aura.

While searching for the abandoned temple, Jaune Arc and Pyrrha Nikos find a cave that they confuse for the temple. While exploring, Jaune grabs on to the stinger of a Death Stalker, believing it to be one of the relics. Pyrrha then runs out of the cave and the Death Stalker follows her out, breaking down some rocks covering the entrance as it does so. Once outside, it flings Jaune, who is still hanging onto the stinger, into the air and Pyrrha flees from the Death Stalker.

The Death Stalker chases Pyrrha to the temple while Ruby and Weiss are carried there by a Nevermore. Upon arrival, they meet up with Yang, Blake, Nora Valkyrie, and Ren, the latter two arriving at the temple via Ursa. The two Grimm chase the eight students to a larger part of the temple where Team JNPR are able to kill the Death Stalker by using a plan devised by Jaune: hacking off its stinger and then hammering it into the creature's head.

Meanwhile, Team RWBY were able to defeat the Nevermore by using Gambol Shroud as a giant slingshot to launch Ruby at the Nevermore. Using Myrtenaster's Dust capabilities and the recoil of Crescent Rose to propel herself, Ruby successfully beheads the creature after dragging it up the face of a cliff. The defeat of the particularly fearsome Grimm using the plans of Jaune and Ruby led to them being made the leaders of their respective teams.

In the first class of Grimm Studies, Weiss, in an attempt to prove herself superior to Ruby, volunteers to take on a Boarbatusk in a class demonstration. In the battle, the Boarbatusk manages to disarm Weiss, but she eventually retrieves Myrtenaster to both block and kill it.

Later on, in the Forever Fall forest, it is revealed that there are larger Grimm creatures of the same name, although in The Emerald Forest, a larger than normal Beowolf was briefly seen. In Forever Fall, Pt.2, a much larger Ursa was seen attacking Cardin. Unlike the smaller ones, it had many larger spikes and armor plates on its back. However, it is defeated by Jaune with slight help from Pyrrha's Semblance.

Volume 2
After intelligence is uncovered about a White Fang base in the ruined Southeastern block of Vale, Mountain Glenn, Team RWBY, alongside veteran Hunter Bartholomew Oobleck, is dispatched to the Grimm-infested area in preparation for a full scale invasion to confirm the White Fang's base. Before departing, RWBY encounter Team CFVY, who report that the number of Grimm outside the city are increasing, backing up an earlier warning from Ozpin. The headmaster reminded Team RWBY before they left on their mission that that, normally, students as young as them would not be permitted to confront such large concentrations of Grimm.

The Grimm living in the area seem limited to Beowolves, small Nevermores and Goliaths. The latter seem to prefer roaming the wilderness outside of the ruins. While the girls occupy their time with slaughtering the Grimm, Bartholomew seems to prefer to spend his time studying the ruins, the plant life, and the Grimm, when possible. A Beowolf is briefly seen later during Ruby's watch of their encampment. Later, Oobleck informs Blake, Yang and Weiss that there are also subterranean Grimm.

In No Brakes, it is revealed that the White Fang are loading the Dust they've been stockpiling onto a train in Mountain Glenn where they rig each train car to separate and explode at timed locations leading to Grimm flooding the subways, with the last of the train cars blowing a hole directly into the city of Vale, thereby allowing the Grimm to enter the city and slaughter thousands. In spite of Team RWBY's best efforts, the plan proceeds leading to the Grimm attacking Vale. After a long and intense battle, the Grimm are finally driven away through the combined efforts of teams RWBY, JNPR, CFVY, the Beacon Academy teachers Peter Port, Glynda Goodwitch, Bartholomew Oobleck and the Atlas Military droids.

Trivia

 * Grimm wear white masks with red blood trail-like designs, similar to the Hollows from the anime Bleach.
 * The name for the creatures of Grimm may be a reference to the Brothers Grimm or Grimm's Fairy Tales, a famous classic collection of German fairy tales compiled by the brothers.
 * After one of the Ursa is killed by Blake, it began to smoke. This could mean that when Grimm are killed, they will eventually dissolve.
 * The shapes and swirls on Adam's mask are similar to the designs of the Grimm, possibly signifying some kind of connection between himself and the Grimm. It may all be an allusion to Adam representing the Beast of Beauty and the Beast.
 * All of the Grimm creatures vocal sound effects were done by William Orendorff.
 * The Grimm, and the types of them, appear to be either common knowledge or a subject taught in combat schools. This is evidenced by the cadet Hunters being able to identify and name the Ursa and the Death Stalker.
 * As of The Badge and The Burden six species of Grimm were introduced. Such being the Beowolf, Ursa, King Taijitu, Death Stalker, Nevermore and the Boarbatusk. However, in the first episode, during it's introduction, the Boarbatusk was only seen as a silhouette, and was the only Grimm specimen without a proper name. It is later officially introduced in episode 9 as a sketch, and was possibly in the locked cage as well.
 * In episode 9, every Grimm specimen was seen in sketches in Peter Port's lesson.
 * Due to the apparent lack of a white-and-red design on the head of the smaller Nevermore Ruby crashed into during her fall from the Beacon Cliffs, it can be assumed that Grimm receive these features while or after they reach full size.