D wanders through a far-future post-nuclear Earth that combines elements of pulp genres: western, science fiction, horror, high fantasy, H. P. Lovecraftian mythos, folklore and occult science. The planet, once terrified by the elegant but cruel Nobles (vampires), ancient demons, mutants and their technological creations, is now slowly returning to a semblance of order and human control — thanks in part to the decadence that brought about the downfall of the vampire race, to the continued stubbornness of frontier dwellers and, to the rise of a caste of independent hunters-for-hire who eliminate supernatural threats.
Some time in 1999, a nuclear war occurred. The Nobility were vampires that planned for a possible nuclear war and sequestered all that was needed to rebuild civilization in their shelters. They use their science combined with magic to restore the world in their image. Nearly all magical creatures are engineered, with a very small number being demons who survived the holocaust. Despite their technology being great enough to create a blood substitute as food, they still prefer to feed on humans. As such, they create a civilization where vampires and humans coexist, eventually developing the planet into parklands and cities. The society eventually stagnates when vampire technology perfects scientific prophecy, which determines they are at their zenith of existence and thus are doomed to fall, overthrown by humans. The human race was also transformed at this time, with fear for the vampires being woven into the genetic level, and the inability to remember vampire weaknesses such as garlic and crucifixes.
Unlike vampires from traditional lore, the Nobility have the ability to reproduce sexually, although their offspring will permanently cease aging after reaching physical maturity, having inherited their vampire parent's immortality.
D is a dhampir, the half-breed child of a vampire father and human mother, the ideal vampire hunter. He is renowned for his consummate skill and unearthly grace, but feared and despised for his mixed lineage: born of both races but belonging to neither. Often underestimated by his opponents, D possesses surprising power and resourcefulness, having most of the strengths of the Nobility and only mild levels of their common weaknesses. It has been seen in both movies that his power is not only physical, but extends into the magical realm as well. His supernatural powers make him one of the strongest beings in the world, if not the second strongest (second only to his father). However, D prefers his physical abilities, only using his magic in times of great need. Unlike most dhampirs, D is able to live as a "normal" human; however, he is marked by his unearthly beauty and exceptionally powerful aura, and thus rarely accepted by human settlements. In terms of weaknesses, he is randomly susceptible to sun-sickness, a severe type of sunstroke, about once every five years (far less than most dhampirs). D also recovers from it at a rate far greater than other dhampirs. Usually it takes several days to recover from sunlight syndrome, longer if the dhampir is exceedingly powerful, but D recovered in a few hours (around 1–6 hours approximately) despite being one of the strongest if not the strongest dhampir alive. Otherwise, D does not appear to suffer from other vampiric weaknesses usual to dhampirs, being able to physically restrain opponents with his aura and having godlike reflexes surpassing even those of Nobles.
His symbiotic left hand states, in "Vampire Hunter D: Bloodlust: "The three of you became impatient with the heartless Bastet and impaled her on 'The Sword'"'. Speculation on whether "The Sword" is D's sword or not is debatable. It is important to note here, however, that the movie differs sharply from the book it takes its story from, Vampire Hunter D: Demon Deathchase, and future entries in the novel series do not differentiate between Dracula, The Vampire King and D's father, proposing that they are one and the same.
D is the host for a sentient symbiote, Left Hand, a wise-cracking human face residing in his left palm, who can suck in massive amounts of matter through a wind void or vacuum tunnel. Left Hand enjoys needling the poker-faced D, but only appears as needed, rarely witnessed or heard by anyone other than D, yet aware of many of D's thoughts and actions. At all other times, D's left hand appears normal. Besides providing a contrast to D's reserved demeanor, Left Hand is incredibly useful, possessing many mysterious powers such as psychometry, inducing sleep, determining the medical condition of a victim, and the ability to size up the supernatural powers or prowess of an enemy, even beyond D's keen senses. In the first and second novels, Left Hand can also revive D when his physical condition is suffering, by consuming the four elements and converting the resulting energy into life force. This ability even saved D from the usually fatal stake through the heart he received from Rei-Ginsei in the first novel. Left Hand has its own mind and will, and acts as D's guide and sole permanent companion, providing a reservoir of knowledge pertaining to the lost Noble culture. So far, Left Hand's origins are unknown, and it is unclear how they came to be joined. However, some of its nature is revealed in the third book, which features a similar creature; it is implied he was one of the Barbarois (human/monster hybrids) who served in the personal retinue of Count Dracula.
D rides a cybernetic horse with mechanical legs and other enhancements, wields a crescent longsword which looks similar to Yoshitaka Amano's scimitar sword design found in many of his works of art, but the sword has a hefty length, similar to that of a Japanese nodachi. D always wears a mystical blue pendant; it prevents many of the automatic defenses (such as laser fields and small nuclear blasters) created by the Nobility in past millennia from working properly, and allows him to enter their sealed castles. In the novels and game, he also uses wooden needles which he can throw with super speed. He protects his milk-white face from the noonday sun with long black hair, flowing black clothing and cape, and the shadow of a wide-brimmed hat. Though he appears to be only 17 or 18 in the first novel (slowly aging as the series goes on), D's age is unknown (although in the novel Pale Fallen Angel parts I and II, it is made known that he is at least 5,000 years old). His beauty is mesmerizing, often unintentionally wooing women and sometimes flustering men.
Very little is known of D's past and the identity of his parents is ambiguous, but his innate power suggests that his father is an extraordinarily powerful vampire. Regarding D's birth, some Nobles whisper dark rumours about their vampire progenitor, the Sacred Ancestor known as Count Dracula, bedding a human woman called "Mina the Fair" (implied to be Mina Harker). Dracula conducted bizarre crossbreeding experiments involving himself and countless human women or even other vampires, with the only successful product of the experiments being D. D, wanting nothing to do with his father save for killing him, refuses to go by his true name. Instead, he shortens it to the first letter. In Twin Shadowed Knight it is revealed that D has a twin who goes unnamed. The twin states that he and D were born from the same woman in exactly the same conditions.
Dracula's role in the novels is very mixed, appearing both as bane and savior to isolated towns, and deified as a legendary god-king to the vampires, many of whom have never even met him in person. D quotes Dracula's precepts ("Transient guests are we" — implied to refer to the Nobility) in the first novel. Dracula appears both as a lawgiver honored for his intelligence, who showed some interest in preserving humans, and as a ruthless scientist (in the second novel), conducting hybrid breeding experiments with humans in order to perpetuate his own dwindling species. D appears to have encountered his alleged father on at least one occasion, as when at times D reaches a place where the imprint of Dracula's power remains, D remembers Dracula telling him that "You are my only success." Like D, Dracula is portrayed as a mysterious and handsome young wanderer who deals out both life and death. However, in the English dub of the anime, D states that Dracula respected humanity and did not feed on innocent people.