A former member of Dracula's 'Family', Tanya spent decades as a vampire under Dracula's rule, until the sight of Dracula about to attack an innocent child somehow broke his control over her long enough for her to flee from him. Forcing herself to feed on animals despite their disgusting taste, Tanya was able to eventually develop a 'blood substitute' to wean herself off her 'addiction' to human blood, dedicating herself to fighting Dracula, winning some of his other followers over to her side.
After years of searching, Tanya and her followers tracked Dracula to Gotham City, Dracula apparently now unconcerned about whether or not he was caught by them as his followers preyed on the homeless to secretly enlarge their ranks. Having somehow learned the true identity of Batman, Tanya began to visit Bruce Wayne as he slept, secretly biting him to infuse him with the vampire 'virus' while not actually drinking his blood. As a result, Wayne began to acquire the strength and abilities of a vampire while still remaining essentially human, giving him the strength to fight Dracula where Tanya and her followers could not do so as Dracula's pre-existing mental link to them allowed him to command them even if they tried to resist him. After saving Batman from his first direct confrontation with Dracula's vampires- although Batman was forced to save them in return when Dracula tried to command the Others to commit suicide-, Tanya appeared to Bruce in his bedroom to tell him the truth about what they were up against, subsequently revealing herself to Gordon so that the city officials could plan a defence as well.
DeathHaving conceived a plan of attack, Batman lured Dracula's vampires into the Batcave, where Tanya and her followers fought them while Batman retreated up to Wayne Manor. Setting off pre-planted explosive charges, Batman destroyed the cave's walls, exposing the interior to sunlight and destroying both Dracula and Tanya's forces. Although one vampire tried to escape by hiding in shadow, Tanya willingly sacrificed herself to draw him into the sunlight, the two collapsing into dust moments before Batman destroyed Wayne Manor itself.
Although Tanya's 'kiss' provided Batman with most of his vampiric powers, he was turned completely into a vampire in the subsequent final fight with Dracula, Dracula draining the last of his blood before Batman impaled him on a tree that had recently been struck by lightning. Initially able to survive on Tanya's blood substitute, Batman gradually came to the realisation that her serum was becoming increasingly less effective, causing him to wonder if he was a more natural predator than Tanya or if the more virulent 'infection' transmitted by Dracula was responsible for his need for blood. Although he briefly found solace in the arms of Selina Kyle, whose strength and courage reminded him of Tanya, Batman eventually succumbed to his vampire instincts, reflecting as he became increasingly corrupted that he no longer understood Tanya's noble sacrifice.
Powers and Abilities
Like other vampires of Earth-43, Tanya possessed superhuman strength, speed, and stamina, as well as an immunity to most injuries apart from decapitation and a stake through the heart (Although later evidence revealed that the stake merely immobilisies unless decapitation takes place as well). She was also vulnerable to sunlight. Initially dependent on human blood for survival, Tanya was able to develop a serum that replaced her need for human blood, apparently through nothing more than her own self-taught lessons about chemistry and biology. Even after years away from him, Tanya was still vulnerable to Dracula's commands, unable to directly defy him as he could command her and her followers to obey his orders.