The Companion is a parasite that lives in the blood of its host. The Companion is the true vampire. It lives off human red blood cells provided by its host, who must drink blood to fill its need.
It came from The Source, a fountain at Mirso Monastery first encountered in Sacrament by Sarah Ashton. You can read about how it got into The Source in The Companion.
The Companion must be fed every fortnight (two weeks) at a minimum. But if the vampire waits that long, the need is very strong, and he or she risks getting carried away and draining the donor. Vampires who don’t want to risk killing those who feed them, take blood in smaller sips more frequently.
Life! The Companion’s sole purpose is self-preservation. Its urge to life is very strong. Many of the changes it brings about to its host are meant to prolong its life. It also does not want to change hosts.
The Companion rebuilds its host endlessly by regenerating cells. Thus a vampire is immortal (with certain caveats—see below) They heal quickly, even regenerating limbs.
The Companion fights any urge toward suicide. It is almost impossible for a vampire to commit suicide.
The Companion makes its host feel very alive, and powerful. There is a fierce joy that comes of being vampire.
The Companion generates energy which can be called on by the host. Thus vampires have incredible strength, more than any human.
A vampire can draw on his or her Companion to draw a field of energy so intense that light cannot escape. At that moment, vampires cast no reflection in mirrors. When the field becomes intense enough, the vampire can pop out of space and control his or her reentry with a fair amount of accuracy. This is called translocation. A mile or even two is possible. But it does drain a vampire’s strength, so the number of times a vampire can relocate in a short space of time is limited. Objects, or even people can be taken along, but this requires even more energy.
Vampires have very sharp senses. They see well in the dark, and their hearing is more than human.
The energy and urge to life of the Companion makes a vampire exude vibrations which intensify with age. These are detectable to other vampires. Humans feel them subconsciously. Crowds part for vampires and humans find them subtly fascinating.
Vampires have a different scent than humans. They smell of cinnamon and a subtle undertone of something some would describe as ambergris.
A vampire can use energy to influence a human’s thoughts (but not entirely control them). But a vampire can control a human’s will. Therefore a human can, under compulsion, know that they are being compelled.
The Companion can be drugged. It responds to substances in the blood, and its powers are suppressed. This property was first revealed in Sacrament.
It cannot repair a severed head, if the head is separated from the body. This is the only reliable way to kill a vampire.
Without blood, it grows weak, thought it does not die.
The power of the Companion can be overcome by groups of vampires combining their strength.
Men first ingested it from a spring called The Source (link).
To find out how it got into the spring, read The Companion.