Batman & Dracula: Red Rain #1

While investigating the brutal murders of Gotham's homeless, all found with slashed throats, Batman uncovers that the killers are vampires led by Dracula, who remains alive through dark powers. He allies with Tanya, a rogue vampire who escaped Dracula's control after witnessing the innocence of a child. Tanya developed a blood substitute and retained her humanity, even after biting Batman to save his life. Together, they battle Dracula’s minions. Batman lures them into the Batcave, where Tanya and her allies stall them while he destroys the cave with sunlight. He defeats Dracula but loses his humanity, becoming an eternal vampire Batman.

Key Details
-Batman's debut as a vampire

-The first standalone, prestige-format installment in a trilogy featuring Batman's battle against Dracula