You turn Juliet, then watch her go to town on Martin.

You'd love to watch the look of jealousy and betrayal in Martin's eyes as you fuck his girl senseless. You rush forward. Martin spots you the moment before you slam his head into the wall, rendering him ****. Juliet screams and recoils away from you.
"No! Stop!" She yells.
"Wait!" You respond, holding up your hands defensively. "Don't you want to become like me too?"
"Of course not you monster!" She shouts. You grin smugly, and lean back, popping your penis from your pants. You show off your impressive, beautiful body. "Do I really look like a monster?" This makes her hesitate.
"You saw Gwen turn Clarice, right? Well did it looks so bad? Clarice is fucking hot now! And she'll stay that way forever. We're immortal! And strong , fast." You stroke your cock. "And very sexy."
You can see the battle of her morals in her face. You extend a hand. "One sweet, orgasmic bite, and all this could be yours." She looks at your hand, extending her own... but hesitates at the last second.
"What about Martin?" She says. You smile.
"You can turn him yourself." This seems to allay the last of her fears, and she slowly takes your hand. You pull her in close, kissing her passionately. You reach down and pull her tunic over her head.
"Wait we don't have to..." She says, glancing at Martin.
"Oh but we do darling." You say, unbuttoning her jeans. She looks distraught but doesn't resist. You push your tongue down her throat, and stare her down lovingly.
"Come. Show me." You say, gesturing to her bra. She reluctantly undoes it, and steps out of her jeans at the same time. Now she is wearing only her thong, which you snap off with ease. You brush her large areolas as you continue to kiss her, then you turn her around and lick her neck. You put your back to the wall opposite Martin, your cock head already teasing at her labia from behind. You lower yourself down, bringing Juliet with you as you do. You rest her on your penis, pressing deep into her cunt. She squeals and you hold on to her wrists as you begin to press into her. You go this way slowly for a while, then you turn the tables.
"Martin!" You hiss. "Wake up Martin!" He startles awake.
"No Martin please! It's not what it looks like!" Juliet cries.
"Juliet?! Why are you fucking that monster!?" He yells through tears, yet seems unable to move.
"No please! Linus stop I don't want it anymore! Nooooo!" You cut off her scream by sinking your fangs into her neck, her warm blood floods into your mouth.
"Noo stop!" Martin screams. "Let her go!" But, of course, you ignore him. Eventually she falls back against your chest and transforms. Her buttocks grow and press into your belly. You feel her breasts swell in your hands as her navel becomes muscular and well defined. Her vaginal muscles tighten around your cock, and you watch her face, which rests on your chest, change, her fangs growing in her open mouth. She blinks awake, looking up at you with lustful crimson eyes. She locks lips with you then turns her gaze at Martin, sitting up on your cock.
"Oh Martin, it feels so good. When it invades you and makes you something amazing." She gasps and grinds her pussy into you as Martin sobs. She laughs, writhing her body expertly on your cock. Then she leans forward and reaches for Martins pants, pulling his penis free, all while continuing to bounce on your shaft, her pony tail and firm ass bobbing up and down with each stroke. She begins to lick and suck Martin, her long tongue wrapping his width easily. Despite himself, he moans in ecstasy. You feel yourself coming close, so you grab Juliet's ass and slam it down harder onto you. She notices this too, and picks up the pace with Martin, licking, sucking and pumping furiously. Then, as if it were as signal to begin orgasm, she bites Martin's cock, making him scream as he cums, shooting blood and seed into her mouth. This makes you come even harder, and you can feel her tight cunt quivering in orgasm too. That doesn't stop her from consuming Martin's blood ravenously. Finally, she pulls back and smiles at you over her shoulder as she slides off slowly. She walks over to her transformed lover, and flicks his eyelid cruelly. He awakes and looks up at his queen, a sharp smile on his face. She pushes his mouth into her crotch and turns to you.
"Thank you Linus, I'll forever be in your debt." You stand and stroke one tit.
"Consider yourself debt free." You say, and she grins mischievously.