Vampires

Vampires (吸血鬼,) are an immortal race of humanoid beings that feed on the blood of humans. A human who ingests vampire blood becomes a vampire. Vampires have fangs, pointed ears (with the exception of Saitō, who has normal ears) and red eyes (excluding incomplete vampires) Until drinking human blood, a vampire may age and retain his/her original eye color. Vampires do not retain strong emotions from when they were human and gradually lose more of their humanity. Despite being former humans themselves, vampires look down on humans and consider them nothing but mere livestock. They dislike increasing their numbers and rarely turn humans. A vampire's power is dependent upon both age and lineage.

As hemovores, they can only ingest blood and nothing else. Vampires have no sexual desire or body heat. They typically sleep between early morning and noon.

Drinking human blood is insanely pleasurable to them, especially right from the source. Vampires can also enjoy drinking vampire blood, but the details and limitations of this have yet to be revealed. Mikaela lives off of Krul's blood for four years before it is no longer effective at quenching his thirst.

Vampires concerned with anything other than blood are considered to be eccentric. Krul Tepes and Ferid Bathory are considered to be eccentric, and Mikaela even more so. As they have gradually lost their human traits, vampires band together out of their own self-interest and not out of affection or love for one another.

When a vampire is killed, they turn into ashes.

A vampire who starves does not die but rather becomes a demon.

Incomplete Vampire
A human that ingests the blood of a vampire does not become a vampire but rather an incomplete vampire.

An incomplete vampire retains their human eye color but grows fangs, and their strength increases in accordance to the strength of the noble that turned them. Whether or not their ears grow pointed like a true vampires is unknown.

Another difference to true vampires that they have is the fact that they continue aging; they only cease to age and complete their transformation once they drink the blood of a human. As well as halting their growth, their eyes will also turn red.

The only known incomplete vampire in the series is Mikaela Hyakuya.

Despite incomplete vampires not being true vampires, true vampires seem to have no aversion towards them. Mika is seen alongside them several times, and they seem unperturbed by the prospect of an incomplete vampire working with them.

Progenitors
Progenitors are royalty among the vampires. All progenitors are nobles but not all nobles are progenitors. By default, they are extremely powerful and higher ranks even more so. However, progenitors of the same rank are not necessarily equal in power. Sixth Progenitors and above have the right to attend meetings of the Progenitor Council. It is likely that all vampire monarchs are progenitors of an esteemed lineage.

There are only three vampires in the rank of being Third Progenitors, meaning that the number of vampires holding a certain rank is the number of the rank. For instance, there are two second Progenitors (Urd and Saitou [past]) and one First Progenitor (supposedly). There is also four Fourth Progenitor, five Fifth Progenitor, and so on.

Not shown:
 * 17th Progenitor Zane Lindau

Nobles
A human turned into a vampire by a progenitor becomes a noble. Nobles are far stronger than the average vampire and wield superior weapons. There are 20 ranks of nobles.

Common Vampire
Common vampires tend to be weaker than the higher classes but remain stronger than humans. A common vampire with greater battle prowess has influence similar to a lower-ranked noble.

Laws

 * Vampires are forbidden from any meddling with the Seraph of the End. Violation will result in severe consequences.
 * Prior to the Apocalypse, vampires were forbidden from meddling with human affairs. This law was overturned once the human population became threatened, and vampires rose up to save their food supply.
 * In the city, vampires are forbidden from drinking blood directly from a human. They may only drink blood directly while on the surface or on the battlefield. This is because more vampires tend to drink their prey dry than not.
 * Drinking blood from another vampire is forbidden but grants immoral pleasure.
 * Only nobles are permitted to turn a human into a vampire.

Aging
A newly-turned vampire can survive off of their sire's blood and will continue to age until drinking human blood, but this will only work for a limited period of time. Once the vampire drinks human blood, the vampire's biology stops completely, and the vampire grows tremendously in strength and power. By drinking human blood for the first time, a vampire completes their transformation.

Natural Abilities
Vampires have impressive power and regenerative abilities; this increases with their lineage and age. They can easily reattach a limb. Nobles have the authority to turn a human into a vampire if they so choose. Vampires may increase their abilities by drinking human blood at any time.

Their eyesight allows them to distinguish a target several hundred meters away, even in pitch-black darkness.

Weapons
In battle, they use their natural abilities as well as different types of weapons. Second-class weapons are used by common vampires, and are not as powerful as first-class weapons. First-class weapons pierce a vampire's hand and drink vampire blood in order to significantly increase their power.

The nature of the first-class weapons is unknown.

Protective Gear
Vampires most commonly wear armbands on their left arms to protect themselves from UV light. They may also wear rings. This allows them to move under sunlight without harm, although they still dislike it.

Weaknesses

 * They have immense pride and typically underestimate their human opponents or may refuse to work together with vampires of rival factions.
 * Sunlight! Exposure to UV light will create a toxin in their bodies, and vampires must wear protective gear to neutralize this effect.
 * They can be killed if their heads are destroyed. One bullet will not do the job.
 * Cursed gear and enchanted gear used by the Japanese Imperial Demon Army limit their healing capabilities.

Trivia

 * They typically refer to the humans as "livestock" instead of calling them by their names.
 * Yūichirō Hyakuya reads a book in chapter 1, which states vampires are only 7x as strong as humans. Considering a vampire's ranking, this can be a severe underestimation.
 * Krul, Chess, and Horn either have small horns or horn-like decorations on their heads.
 * A vampire's heart doesn't beat any more
 * All vampires can actually turn humans into one of them, but they have this special rules that only progenitors are allowed to do so.
 * Only 5th progenitors and above can attend a progenitors council (except Ferid's case for some mysterious reason).
 * Vampires hearing are so strong that they can even hear the sounds of bugs moving.
 * The first one to get cursed by God is the first progenitor and the curse spread and created more vampires.
 * Vampires don't prefer to increase their own kind because they don't want to share their curse.
 * A vampire's curse is that they can't die for eternity.
 * Vampires wallow in boredom for the longest time, so they yearn for romantic feelings.
 * For a while, Vampires' thought processes are preserved the way they were before they were turned into vampires
 * When vampires want someone they've taken a liking to. To stay by their side, they give their blood to them.
 * All vampires, including progenitors, were once human.
 * Vampires have no body temperature.
 * Vampires have no metabolism and all their biological activity is suspended.
 * The complexity that they had as a human becomes the cornerstone of their identity when they become a vampire.