Carmilla serves as the Queen of Styria and the leader of the Council of Sisters, a powerful coven of four vampires. Her origins are rooted in a deep-seated rebellion against oppressive authority. Turned into a vampire centuries ago by an unnamed male Vampire Lord, she eventually killed her maker, describing him as old and cruel. This act of violent liberation defined her worldview, leaving her with a profound disdain for what she perceives as the tyranny of powerful, mad old men. She joined Dracula's army as a general, but her loyalty was always conditional and masked by her own hidden agenda. She believed Dracula's plan for human extinction was not born of grief, but of madness, and more pragmatically, that it would eliminate the vampire population's primary food source, leading to their own extinction.

Carmilla's personality is defined by her regal, manipulative, and deeply ambitious nature. She is a scheming noblewoman who views those around her as either tools to be used or obstacles to be removed. She is ruthless, sadistic, and takes genuine pleasure in violence, most notably demonstrated when she brutally beat Hector to assert her dominance. Beneath her poised and calculating exterior lies a core of unquenchable ambition and rage. Her desire for power is not merely greed; it is a psychological compulsion born from her past subjugation. She explicitly states that her life has been defined by men taking things from her, and her drive to conquer is a direct response to that trauma. She is not motivated by revenge against a single person, but by a desire to ensure that no one can ever hold power over her again. This leads to an insatiable hunger for control, where nothing less than everything in the world would be enough to satisfy her.

In the story, Carmilla’s role evolves from a high-ranking general in Dracula's war council to the architect of a new vampire empire. She is the primary political and strategic antagonist who successfully orchestrates a coup against Dracula by exploiting the infighting among his other generals. She manipulates the human forge master Hector, a key figure in Dracula's army, turning him against his master by planting doubts about Dracula's sanity. After barely escaping the final battle that defeats Dracula, Carmilla returns to Styria and reveals her true plan to her sisters. Rejecting Dracula's nihilistic genocide, she proposes a more sustainable and tyrannical system: to conquer a vast territory in Eastern Europe, fence it in, and treat the human population as livestock to be farmed for blood for centuries. Her role in the final season shifts to that of an increasingly isolated and paranoid ruler, whose grand vision ultimately becomes her downfall, drawing the wrath of Isaac, another of Dracula’s former generals seeking revenge.

Carmilla's key relationships are complex and instrumental. She forms the Council of Sisters with her three closest allies: Striga, a warrior; Morana, a strategist; and Lenore, a diplomat. While she leads them, she considers them her equals and family, relying on their skills to execute her plans. However, her growing ambition strains these bonds, isolating her from them. Her relationship with Hector is purely exploitative. After manipulating him into betraying Dracula, she drags him to Styria, beats him into submission, and declares him her slave, intending to use his forging abilities to create an army of night creatures. In contrast, she operates as a direct adversary to Isaac, the forge master who remains loyal to Dracula. He invades Styria specifically to end her life, viewing her ambition as a corruption that must be cleansed. Her dynamic with Dracula is one of contempt and calculated betrayal; she views him as just another cruel, senile old man who has outlived his usefulness.

Carmilla undergoes a distinct and tragic development arc. Initially presented as a cunning and strategic pragmatist, she is the only general who questions Dracula's suicidal war against humanity. However, after successfully seizing power and returning to Styria, her ambitions begin to spiral out of control. She grows from a regional schemer into a megalomaniac obsessed with conquering the entire world. This growth is a corruption; she becomes increasingly impatient, paranoid, and detached from the counsel of her sisters. Her behavior starts to mirror the very thing she once hated in Dracula and her former master. In her final stand, cornered and exhausted after fighting off waves of Isaac's night creatures, she refuses to be killed by a man. Denying her enemy the satisfaction, she impales herself on her own sword and self-destructs, asserting control in the only way left to her.

As a vampire, Carmilla possesses a formidable array of supernatural abilities. Her most notable assets are her superhuman strength, speed, and agility, which she demonstrated by slaughtering dozens of powerful night creatures in rapid succession. She also wields a signature curved blade with immense skill, making her a terrifying combatant. She has great endurance, surviving prolonged and brutal engagements. While she does not display overt magic like Dracula or Sypha, she shows knowledge of the supernatural, correctly deducing that Dracula's castle had been teleported. In her final act, she demonstrates the ability to self-destruct, creating a massive explosion that destroys a portion of her castle. Beyond her physical powers, her greatest abilities are her charisma and intellect; she is a master manipulator capable of sowing discord and turning allies against one another through pure force of will and cunning dialogue.