Vampire

A vampire (吸血鬼) is a creature that relies on the blood of humans in order to sustain itself. There are two types of vampires, but only one actually needs to drink blood, the other merely likes to but loses control if they do. The two types are:


 * the True Ancestors, who were a blood-sucking species to begin with
 * the Dead Apostles, who became a blood-sucking species

Vampires
Vampire is the general term for those who suck the blood of humans; it includes the blood-sucking species that is Dead Apostles as well as those that aren't Dead Apostles. In the Tsukihime setting, a vampire sucks the blood of humans to maintain their own body. If the vampire gives the human his own blood in the process, the human will not completely die. A normal human will end up dying, but sometimes, there are those whose body has a high potential, and if his soul has a good capacity, he can remain in the present world.

Several years after the death of the body, the brain dissolves and the soul is freed from the cage of the body; and from corpse eating ghoul, it becomes a moving body, a living dead.

Ghouls sleep in their tomb to replenish their body, and slowly reconstruct their flesh by eating corpses. then, after a few more years, they can recover their brain and memory, and can be called "vampires".

Those who became vampires can move on their own free will, but they cannot escape the rule that has them supply blood to their vampire parent. After growing accustomed to living in darkness after some more decades, the vampire still follows his vampire parent but can give their own blood to a human and have their own followers.

To stop that eternal cycle, the Church has built the Burial Agency, to hunt heresy and destroy the Dead Apostles. The purpose of the Burial Agency is the extermination of all vampires as well as the sealing of the founding 27 Ancestors.

Source: Tsukihime Dokuhon PlusPeriod dictionary entry (p.178)

Blood-sucking species
Blood-sucking species (吸血種) is the general term for those who suck the blood of others. Originally, it was used indifferentially for vampires as well as other blood-sucking species, both having a similar meaning. Those who suck blood can be found all over the world with subtle differences, so this term is preferred. In that regard, Akiha is from a blood-sucking species.

The difference is in the facts: the enemies of the Church are vampires; that is, Dead Apostles and True Ancestors. For that reason, they do not care about the blood-sucking creatures from South America or from the continent. Good for you, Akiha.

Source: Tsukihime Dokuhon PlusPeriod dictionary entry (p.178)