Frost

Frosts (凍 (フロスト), Furosuto; Japanese for "Frozen") are supernatural beings that originated from the. In contrast to, whom are beings whose hearts have been hollowed out from within them, the Frosts are whose hearts have been 'frozen over'. It is believed they were originally a tribe of ancient who closed off their hearts out of fear that they would lose their hearts to despair and become mindless Hollows just like those around them. In the process, however, their tribe became 'just like ice and snow itself', cold and unfeeling; they were no longer alive but neither were they dead. They had evolved into some sort of inhuman existence bordering between life and death.

Powers
The core of a Frost's power is called "Everice" (永遠氷 (エバーライス), Ebaraisu; Japanese for "Eternal Ice"). It refers to the fact that the heart of a Frost is akin to ice itself. They do not possess heartbeats nor do their bodies project warmth; they exist in a state of death constantly despite being alive. According to legend, the original Frosts were a tribe of humans who become filled with terror at the sight of their own fellow humans becoming these monstrous Hollows after losing their hearts to despair and regret. Desperate to circumvent this fate of theirs, they engaged in rituals in which they could freeze their hearts so as not to become consumed by their own human emotions. However, in the process, they had lost their humanity and became creatures that could neither be called alive nor dead. Rather, they existed as some form of inhuman life, resembling a state of immortality in some ways. While they could be killed, it was believed that because their hearts were frozen over, even in death they would be unable to enter the flow of souls. For a Frost to die means to disappear from this world forever. Of course, there are those that speculate that some Frosts, in their final moments, may experience warmth again after a lifetime of coldness; their hearts finally melting and allowing them to return to the circulation of souls.

Unlike Hollows, Frosts do not possess. At least, not in the traditional sense. Normally, reiatsu flows outwards from one's heart. As long as the heart remains beating, reiatsu will continue to flow endlessly. But the Frosts are beings whose hearts do not beat in the normal sense of the word. As hearts that are frozen over, it means that reiatsu cannot flow naturally from them, and as such, Frosts are beings that do not emit spiritual pressure. In place of a pressure, their spiritual presence instead causes all warmth to be sucked out from the surroundings, whether they be living or not. Entire lands become nothing but frozen tundras simply by a Frost's existence. While some Frosts cannot control this phenomenon, others have learned to harness this innate power of theirs and only release it on their own whims. It is often said that Frosts possess 'Frozen Reiatsu', in that they do emit something that can be recognized as spiritual pressure, but that it does not register to the as such. If reiatsu can be likened to a flowing body of water, a Frost's spiritual pressure would be a frozen ice lake.

Behind the Scenes
This concept was inspired by the Others from the novel series, A Song of Ice and Fire. It was originally meant to become a concept heavily based on the Yuki-onna from Japanese mythology, but rather than simply importing that concept over to Bleach, the author instead opted to develop a species that resembled them and perhaps could even be alluded to them, but ultimately were their own unique concept within the Bleach universe.