True Ancestor

Unique existences even among the vampires, the True Ancestors (真祖) are nature spirits (akin to the Elementals) of such great magnitude that even normal human can perceive them. Vampiric creatures from birth, however unlike the Dead Apostles and other blood-sucking species the root of their bloodlust is psychological rather than physical. Also, because they are also part of nature, they can use the power of Marble Phantasm to change the world around them accordingly to their thoughts. They can be classified as a type of large fairy.

Origin
At an undetermined point of time in the past, Gaia, the incarnation of the planet, suffered with the indiscriminate corruption that humans caused in the environment. Because at the time it lacked the means to defend itself from humans, Gaia sent a plea to the other celestial bodies for help, on the criteria that only a planet is able to correctly judge another of its kind.

The one who answered Gaia’s plea was Brunestud of the Crimson Moon who offered a pact to the planet: in exchange of being allowed to live on Earth, Crimson Moon would allow the creation of a self-defense mechanism for the planet based on him. From this pact between the Ultimate One of the moon and the spirit of the Earth the True Ancestors were born as a Counter Force with definite form, created for the purpose of returning the planet to its original state, before the corruption caused by humans.

Despite their origins as anti-humans entities, Alaya does not see the True Ancestors as targets. That is because the True Ancestors are extensions of the world, mediators of nature, before being enemies of the humanity. However, differently from Divine Spirits, they are supernatural beings born from the world without the interference of people. That which is desired by the planet but not by humanity is bound to fade from the observable world and decline in numbers. When Arcueid Brunestud was born in the 12th Century, the True Ancestors had decreased to a mere 100, from which the majority were killed when the White Princess went berserk.

While the birth of a True Ancestor goes along the lines of a natural phenomenon that happens when needed, Arcueid’s case was more of an artificial occurrence premeditated by the others True Ancestors. Their reason behind this was quite simple: they wanted the advent of a stronger, more perfect existence that would be capable of hunting down their fallen brothers (the Demon Lords) and their renegade children (the Dead Apostles).

There is only one known case of a child being successfully born between a True Ancestor and a human.

Nature
While being born from nature just as any natural spirits, the True Ancestors are fundamentally copies of the Crimson Moon with minds and bodies modeled after humans, the latter done so under the principle that it would be best for them to resemble those who they are supposed to rule over. Because Crimson Moon was their basis, the True Ancestors not only turned to be detached from nature’s desire of protection from humans but also inherited a terrible flaw from the original: vampiric impulses.

A purely psychological impulse that pushes them to suck the blood of others, because there is no physical reason behind those impulses there is no definite cure for them. Thus, the True Ancestors need to sleep through their childhood until they are mature enough to have self-control. From that point on, the True Ancestors must use their own powers to keep the impulses in check. That is why, even though they have the capacity to manipulate nature at will, they never fight at 100% as most of their powers is already being used to restrain themselves.

However, because there is no end to the vampiric impulses, they do not disappear and instead accumulate with time. Eventually, those impulses will become too powerful to be restrained and threatens to take over. The only choice left in this case is for the True Ancestors to fall into a deep, eternal sleep. This can be said to be the limit of life of those without a definite lifespan.

There is also the case of the Demon Lords, True Ancestors who succumbed to their vampiric impulses and started to drink blood indiscriminately. Because they no longer need to restrain themselves, the power of these fallen Ancestors is said to be overwhelming to the point of being said that they cannot be defeated with the power of humans, and even the other Ancestors have troubles dealing with them.

Prior to his death, Crimson Moon took providences to make his return possible. All True Ancestors have a Reality Marble implanted within them. Whenever a True Ancestor attains a level of power close to the original, this implanted seed will allow Brunestud to take over his body. Still, because all True Ancestors are born with the fundamental flaw of bloodlust, he needed to create more perfect successors. Arcueid and Altrouge are apparently two of such attempts.

Among the True Ancestors, those who could manifest the Millennium Castle, through their Marble Phantasm ability, were given the title of Brunestud and regarded as royalty. This is the reason why the True Ancestors call Arcueid, who is considered the only successful clone of Crimson Moon, the princess of the True Ancestors. There is also the case of the half-breed princess of the Dead Apostles, Altrouge Brunestud, who is born from a mix between a True Ancestor and a Dead Apostle. She lacks the normal powers of a True Ancestor, and thus cannot use Marble Phantasm to summon the Millenium Castle or move from one place to another by recreating her body, but she is capable of summoning the Crimson Moon. That is the reason why she is one of the two possible successors of Crimson Moon and why she has inherited the name of Brunestud, but she is generally considered too "unstable". These two are also the only remaining Ancestors alive and active by the time of Tsukihime

True Ancestors with a female body are rare, probably because the original Crimson Moon had a male body.

They don't dream, but in Arcueid's case, she must dream a little since her meeting with Tohno Shiki.