Grimm is an old nickname for death, and this will tell you enough about these men. They are the ones who oppose Death, who break it and fight it.
Grimmbreaker refers to a healer who uses his arcane skills to mend wounds. They are members of the Order of Fluids, though hold no direct ties to the Church.
The Order of Fluids was an Order founded at the end of The Age of Plagues, during which an Eastern Blight thinned much of the Narvasi Empire’s population. A Council of Healers was founded to bring together all knowledge of medicine and disease. These ranged from Witchdoctors who use blood to improve the potency of their cures, to Wilder Shamans who claimed the best method for healing involved artifacts made from animal and human bone.
The Council of Healers tested and tried every method presented to them. Realizing all medicine could be boiled down a study of fluids, They formed the Order of Fluids. Many methods were considered dangerous or simple superstiion and were banned by the Order.
This led to a purge of quackery with many who held harmful believes ending atop a pyre or at the end of a Blacksteel Sword.
Members of the Order of Fluid would travel town to town with healing draughts and enough knowledge to help someone with a fever or to bind a broken leg.
Grimmbreakers were the elite members of this Order. Capable of using their knowledge of the Arcane to speed up healing.
The core rule of arcane healing is that one cannot push the body beyond its own limits. While a broken leg can be forced to heal in minutes, an amputated leg will never be grown back.
Healing falls under the school of creative magic. The rule of Balance states that in order to avoid going mad you have to avoid tapping into your own source of energy.
Therefor the energy to heal is drained from other living creatures, which results in their death. This includes rats, dogs, cats and humans near death. The further the healing strays from what the human body can do, the more energy is required.
Even by keeping a balance creative energy has an effect on the mind. The more someone acts out creative feats, the more this person begins to urge for the opposite. For destruction, deconstruction, suffering and so on. This is why Grimmbreakers often hunt for the animals to use in their healing rites.
A Grimmbreaker, especially a good one, is cold and calculated and unpleasant to be around. They are so focused on their purpose that they forget how to be human.
As the constant battle with Death is a costly one, Grimmbreakers are not cheap and are rarely open for charity. They’ll take their payment whether you want it or not and being in debt with one can lead to unpleasant circumstances.