Retribution.

This little bitch kept you from Sarah, and for that she will pay. You pull her up by her neck and lean in close.
"I'm going to fuck you with my fangs for what you did to me." She blubbers but says nothing. You let go of her neck and angrily tear her sweater from her torso, making sure to dig your fingers into her flesh and pull her shirt with it. She screams and stands half naked before you, small pinpricks of blood from your fingernails dot her nonexistent breasts. You take a knee and bend her over it, then you pull her skirt off, to reveal her functional panties and flat arse. You grab her underwear, fingernail digging into her asshole as you do, and tear it away, giving you a view of her bare flesh. You begin to slap it, lightly at first, but then with increasing intensity. She sobs louder with every hit, her ass cheeks quickly becoming bruised and red. You lean down to her ear.
"Now, apologise." You say menacingly.
She sobs and swallows, so you place a hand on her ass threateningly.
She sobs one more time; "S-Sorry! I'm sorry!"
"Sorry for what?" You hiss.
"Sorry for... keeping Sarah from you." You grip her cheek, then release.
"I don't forgive you." You say. "Maybe you can give me a real apology once you've had your training!"
She jerks around in panic; "Wha-? Wait!" but you are already darting for her neck. Your fangs penetrate her throat with a satisfying crunch and her warm blood flows into your mouth. You turn her over so she is laying on the floor and you loom over her. Each gulp of her sweet warm blood fills you with ecstasy, and renewed vigor. Quickly, it is over, and Keira lays before you, her body convulsing in transformation. First, breasts grow on her chest, to a reasonable size too. They are perky, round and perfect. Her undeveloped thighs and ass grow larger and firmer, her pussy now much more visible in her new thigh gap. Her hair loses its dull colour and gains a deep golden lustre. Her fangs grow between her plump lips, and finally she opens her glowing golden eyes, a look of sorrow on her face.
"Oh no!" She says, straightening up, sadness dominating her expression. "This is what I have deprived Sarah of?" She looks up at you, eyes filled with regret and tears. "How can I ever receive your forgiveness?" She kneels before you, new breasts jiggling.
"Well." You say, arms crossed. "With the appropriate punishment I'm sure I could find my way to forgetting this little incident."
She looks up at you and says sincerely: "Yes of course. Do to me whatever you require."
You clamp her head with your hands, and push her waiting mouth over your cock. She maintains eye contact with you, being sure to keep up her steely gaze. You push in, face fucking her harshly. You notice a finger reach for her groin.
"Don't you dare you little slut. You're not allowed to come til I tell you you can." She pulls her hand back reluctantly and grips her thighs. You push in harder, slamming your cock down the back of her throat. Any human woman would be gasping for air, but Keira's vampire body takes it with ease. You begin to shoot your load, cumming into her mouth as you continue to fuck her face brutally. She swallows each spurt dutifully, never flinching or losing eye contact once. You pull out and spray it on her face and tits. She takes it, the white liquid rolling off her statuesque body. You push her down and insert your penis into her sopping cunt.
You growl; "No one said you could get wet." She continues to keep eye contact, trying to remain sincere and professional, but you can see the glint of lust in her eye. You pound her, your member smashing her vagina again and again. She bites her lip as she tries not to come.
"Tell me what you are." You hiss.
"I'm your vampire whore." She whispers back. "I'm you're fucktoy, you're cum rag, you're plaything." You shoot a massive load into her vagina, then pull out spraying her crotch with your seed. You observe as the white liquid oozes out of her pussy. Then you flip her over to reveal her round ass and inviting sphincter. You push in, her body gripping you tightly. You begin to pound again. You see her balling her hands into fists, suppressing her orgasm with all her vampiric might. You pull free, spraying her back and ass with your final orgasm. You stand and she turns to look at you.
"Now." You say, slowly. "You may cum." She screeches as she releases, her cunt quivers sending waves through the rest of her body. Her hands smear the seed on her breasts and her tongue tastes the cum on her face. Eventually, she subsides, and smiles at you for the first time. You gesture to the fire door. Together, with some effort, you wrench it free.
"Very well." You say. "You are forgiven. Go get yourself cleaned up and meet our compatriots in the basment."
Keira nods and says; "Thank you master, and that Sarah... you will enjoy her well I am sure. She is very special."
You nod and watch the vampiress walk away, her tasting your seed as she does. Then you turn and enter the night.