Bite-Sized Monster Dictionary
Often mentioned in the folklore of various cultures: a monster that sucks the blood of humans and livestock. Possesses high battle capabilities and is not easy to kill. Its strength is the greastest among monsters. On the other hand, vampires have many weaknesses such as being afraid of rosarios and water. Also known as the Immortal Ones.
Appearance
The appearance of a vampire can vary greatly, but all vampires have razor-sharp fangs. Some vampires have retained a 'lost' ability to change their form. A vampire in its sealed state will (at the very least) have the color of its hair changed, but in Moka's case the size of her bust has been slightly reduced when sealed.
Other vampire type(s)
Another type of vampire known as a Shinso was originally a vampire but absorbed other ayashi & evolved. You can technically count a Ghoul like Tsukune Aono as another type of vampire (due to Moka Akashiya injecting him with her blood thus originally making him a temporary vampire but now a ghoul). As Yukari Sendo mentioned there being the existence of Dhampires or Danpi-ru.
origins &/or history & obsolete rules
"A monster of legendary strength... that permanently infuses his own body with energy. If he is pure-blooded, his combat abilities stretch well beyond imagination. They live apart from other creatures, either human or monstrous, for they are feared by everyone." - Ruby's witch master.
Powers & Abilities
The abilities of vampires can vary as much as their appearances can. Some vampires (Kahlua) can change its form at least partially. Other vampires use odd weapons as a form of offense. But other vampires retain a simple fighting style which works best for them. Vampires have a "Youki Detector" that surpases all other ayashi. This ability allows them to sense youki and killing intents of nearby ayashi.
The most significant ability that Vampires possess is their ability to turn their youki into raw power/strength, which is an ability no other Ayashi possesses. This ability, though not fully described, appears to be an advanced and highly-developed variant of the fairly common ability of Ayashi to enhance their physical attacks or generate a specific attack by gathering, compressing, and honing their monstrous energy and unleashing it in a single burst.
Vampires, due to being the strongest of monsters, have a very large resevoir of youki/monstrous energy, and when they channel, compress, and hone this energy for battle, the energy is generated at a level that is equivalent to another monster's fully power "special attack." This would correspond to another monster performing a specific technique and applying the highest concentration of Youki that they can generate at a time, and discharging it in a single instance.
Vampires can generate this kind of power continuously in battle, due to their vast reserves of energy and their enhanced energy-to-strength conversion process, where they are able to fight with what is the equivalent of a continuous stream of full-power special attacks.
This fairly simple but tremendously powerful ability seems to function as a kind of kinetic booster effect, i.e. amplifying the user's physical strength, and appears to also possess a transmission and incendiary aspect as well. It is often accompanied by a strong bursts of Youki and flares of the Vampire's aura, which is best illustrated with Moka Akashiya's attacks. Finally, the ability appears to be very instinctive in nature, and is scalable across the full spectrum of the Vampire's abilities, such as normal movements and tasks.
Weaknesses
As being one the most strongest monsters, they also have the most weaknesses such as water, crosses, etc (depending on the version of vampire & vampire myth).