Stories of Vampires were popular long before Twilight made these magnificent beasts sparkle, and they still continue to be a great source of inspiration for many supernatural Anime - thankfully, minus the bling factor.
The most generally accepted vampire mythology claims that these creatures were once human but, through a transformation initiated through blood exchange (and consumption), become undead beings with superhuman abilities. However, vampires are no longer only portrayed as evil, with many Anime series putting their own unique twist on traditional vampire tropes, with epic results.
Seras Victoria: Hellsing
There are two types of vampires in the Hellsingvampire lore, namely Purebloods and artificial vampires - laboratory creations made by the Nazi aligned Millennium Organization. As the story goes, the only humans that can transform into vampires are virgins, who have to be drained of all blood by a vampire of the opposite sex. If said human's virginity was, in fact, not intact, they would ultimately become a zombie-hybrid known as a ghoul. Before Seras Victoria had undergone the transformation, she worked in the police force, forming part of the team sent to investigate a rogue priest from Cheddar Village.
The holy man was actually an undercover vampire set on building an army of ghouls, starting with the Village's residents. The devious priest manages to take Seras hostage, intending on adding her to his ghoul army - until the great pureblood Alucard appears. After confessing her celibacy, Seras is severely wounded by the priest (who has no use for virgins) - but she is granted a second lease on life after Alucard offers to turn her into a vampire. Already possessing a background in law enforcement, Seras is quickly recruited by the counter-terrorist Hellsing Organization and becomes Alucard's right-hand lady.
Shinobu Oshino: Bakemonogatari
In Bakemonogatari, vampires not only consume the blood of a human, but also their flesh. Their diet is also not limited to humanity, as they regularly snack upon supernatural beings known as 'oddities'. Before Shinobu Oshino became a vampire, she was a young princess named Rola who lived under a tragic curse that inspired those around her to take their own lives, in an unwarranted and extreme declaration of their affections.
Forced to flee her kingdom to save its residents, Shinobu traveled the lands, careful to always be on the move so that she doesn't cause any further mass incidents. During her journey, she comes across a vampire named Deathtopia Virtuoso and requests to become a vampire herself, in an attempt to break the gruesome curse. Her wish fulfilled, she presents herself in the form of an eight-year-old girl and becomes known as Kiss-Shot Acerola-Orion Heart-Under-Blade, the first vampire to settle in Japan.
Alucard: Castlevania
Castlevania tells a more traditional tale of Dracula who is found by a beautiful human, Lisa, and the two quickly fall madly in love. After their son's birth, Lisa encourages Dracula to travel the world, after being cooped up in his castle alone for so many years. Upon his return, Dracula finds that Lisa had been wrongfully burned as a witch, and the distraught Vampire King seeks vengeance on all humanity - unless his only son can stop him.
Adrian Tepes, better known as Alucard, is the ultimate human-vampire hybrid. Possessing most of the powers of a vampire, he seems to not be perturbed by bloodlust, capable of surviving quite happily on human food (fish apparently being his favorite). Having inherited more of his mother's personality, Alucard is dead against his father's plans but was easily defeated after attempting to intervene. Dracula injured Alucard so severely he that had to go into a deep hibernation state in order to recuperate. After a year's reprieve, the hunter, Trevor Belmont, and scholar, Sypha Belnades seek out his aid, and together, the three unlikely companions join forces to take down the King of Vampires.
Saya Otonashi : Blood+
Chiropterans are ancient bat-like creatures that survive off of human blood - and Joel I and Amshel have found a mummy that appears to resemble such a beast. Clearly having never watched a single horror movie, the scientists foolishly remove two cocoons from the corpse and prompt them to hatch by dripping blood on them. Surprisingly, two infants, seemingly human, emerge and Joel and Amshel decide to raise them separately to test the age-old theory of Nature vs Nurture.
Saya is the luckier of the two, living out a relatively normal human life, while her twin, Diva, is the subjected to countless experiments. However, Saya seems quite ill, as she has very limited memories and has to regularly receive blood transfusions to stay healthy. Unaware of her vampire heritage, Saya unintentionally turns her childhood companion Hagi, into her chevalier, unwittingly creating a source of chiropteran energy for herself in the process. After spending a year living in Okinawa as a youthful human, Saya begins to become more aware of her supernatural capabilities - as well as her feelings for Hagi.
Zero Kiryu: Vampire Knight
Zero Kiryu is another character with his foot on both sides of the fence, being a vampire as well as a vampire hunter in this classic shōjo Anime series. The story is set in the Cross Academy, a school that caters to both human and supernatural students. As a Guardian of the Academy, Zero is responsible for maintaining harmony between the Day (human) and Night (vampire) Classes.
Zero lost his humanity at the hands of Shizuka Hio, who also murdered his entire family, finding no use in reanimating their corpses. After being trained by Toga Yagari, Zero slowly finds his place in this new supernatural world, however, his struggles are intensified by his unusual intolerance of blood tablets. These pills are used by vampires as a blood substitute, however, Zero's thirst is incessant. Thankfully, his good friend Yukia Kuran offers her blood as nourishment - subsequently sparking furious jealousy from the infatuated Kaname Kuran.
Most modern vampire Anime stories seem to analyze the relationships between these supernatural beings, emphasizing that the world is not simply divided into black and white, or good vs evil. Despite their demonic origins, vampires can overcome the natural urge to kill, forming civilized societies where humans and the undead can (generally) co-exist. Some even go so far as to become heroes in their own right, protecting defenseless humans from their bloodthirsty kin. Avoiding the path of evil is not always easy, and takes a bit of extra dedication for some, but as they say, nothing good comes easy.