No, I obviously do not own Harry Potter. I don't think Ms. Rowling would approve of this anyways...
On a side note, the Fenrir I was picturing in this is a bit more like Pete Steele (look him up) than that from the movie.
Carry on, smut lovers...
"Bellatrix," he crooned in her ear, creeping up on her from the shadows of the woods.
"Fenrir," she snarled in response, spinning to face him. "What took you so long?"
"I got hungry, love." She rolled her eyes at him, stubbornly crossing her arms.
"I'm not your love." He gave her a vicious smile, wrapping a brawny arm around her slim waist. His tongue trailed up the side of her arching pale neck, and she couldn't help but let out a pixie-like giggle.
"Why don't I try to convince you otherwise?" he purred, and with the gut wrenching jerk of apparition, they were in Bellatrix's bedroom. She looked at him with massive eyes.
"But… If Rod were to appear…" she babbled.
"It just makes it all the more exciting, don't you think?" he growled softly, and a thin smile slowly spread across her angled cheeks. Fenrir crept around her and began loosening the corset ties on the back of her black dress, taking every opportunity he got to drag a sharp nail down her pale white flesh, making her shiver and let loose a short twinkling laugh each time. When he had unlaced her, he let his teeth gently graze the exposed skin of her neck, then turned it in to a tender kiss.
She pulled away, sliding the dress down her slim body and exposing all of her, uncovered, like a white lily blooming from the darkness that consumed her being. She stroked her white fingers along her thin body, pausing and playing in places that made Fenrir grunt in approval. He took a step towards he, but she took a step back, placing her hand in the center of his chest, keeping him at arm's length.
"I don't want it gentle tonight. I want you to tear me apart. Make me scream." Fenrir's breathing grew heavier at her words, but he stayed where she stopped him as she slid onto the bed. She lay on top of the covers, and as Fenrir undressed himself, she stroked between her thighs, already glistening with anticipation. He watched her, leaning against a post of the canopy bed at her feet, fully nude. She watched his manhood, fully erect, sway. It was one part of him that didn't lose its animalistic qualities when the werewolf changed back to his human form. She hungered for him, ached for him, but the torture of waiting was just as sweet, as they both knew.
He rubbed his palm down his length, making Bellatrix smile and delve a finger deeper inside herself. When she withdrew it, Fenrir snatched up her hand, sucking it clean. Her hips swayed in response, and a grin split his face as he grabbed her ankles and wrenched her up, pulling her towards him. He kneeled on the ground as her legs hung off the edge, looking up at her from between her thighs with a wicked glint in his eye. Working his way up her legs, he bit her gently, then got harder as he drew closer to her core, already making her squirm. By the time he got to the hollow of her thigh, he had drawn blood several times, which he eagerly lapped up. He hovered teasingly at her entrance, making her snarl at him.
"Do it," she moaned, grabbing a handful of his hair and trying to force his head down.
"Now, that's not very nice," he purred, and she nearly hissed at him.
"Fine, I'll do it myself," she spat, and her hand snaked down her stomach until her index finger found her spot, and she worked it viciously.
"Impatient, are we?" he teased, and bit her finger hard. She yanked her hand back with a yelp, and with a smile he forced his tongue into her, flicking it with unmatched expertise. She moaned, and dug her nails into the werewolf's back. He grabbed her bony hips, forcing them to be still as she bucked them, until she was reduced to just arching her spine at an almost inhuman angle. He nipped at her folds, making her let out short gasping screams, until she contracted around him and lost all air in her lungs altogether. He kept licking her until she finally got enough breath to scream, and she let out a long expletive, digging angry red trails into his back. She had to grab him by the hair and drag him off her, because her orgasm just kept coming and he was too stubborn to let it stop. She dragged his head up to hers, kissing him and tasting her own juices on his lips.
"Fuck me," she snarled, and he let out a lusty grunt, clamping his hands on her thighs possessively. He grabbed her and nearly threw her onto her stomach. She clamored up and put her hands on the head of the bed. Wordlessly, Fenrir took the canopy and tied her wrists tightly to the edges of the bed, forcing her chest down and her rump to be presented to him. He grabbed it and dug his nails in, making her groan into the pillow, and he slid his length into her smoothly. She sighed in satisfaction as he filled her nearly to bursting, with just the slightest edge of pain that made it so delectable. His hips moved in perfect rhythm, stroking her perfectly. But it wasn't what she wanted.
"I didn't say make love to me," Bellatrix growled, "I said fuck me." Fenrir snarled at the challenge, and his thrusts grew harder, deeper, and faster, and he cupped her breasts in his hands, dragging his nails down her torso. She tightened herself around him, intensifying every sensation, until Fenrir had to gasp "Stop. I don't want to go so soon…"
He pulled slowly out of her, then flipped her harshly over again, so her wrists were crossed over her head. He grabbed her ankles and threw them over his shoulders, then leaned into her until she was almost bent double. He shoved himself into her, and she clamped her legs tight around his neck, making herself even tighter than she was before. He grunted, but just moved faster. She knew he wanted to come. He changed to shallow strokes, brushing the spot within her that made her let out short high-pitched moans until they once again changed to a wail as she clenched around him. His thrusts became wilder, until he let out an animalistic grunt and spilt himself within her, filling her so that it dripped out of her and onto the wrinkled bedspread. He collapsed onto her after his forehead uncreased and his panting stopped. With a labored last grunt, he rolled off of her and onto the floor with a heavy thud. She watched him with detached curiosity as he dressed, running his hand through his hair as he stretched.
"Your place next week?" she asked.
"Sure," he responded with a wink, "Whatever you want, love." He began to walk out the door.
"Wait," she called, "I'm still tied." He turned to look at her, naked and glistening with sweat.
"Well, what do you know, you are." He continued walking after giving her a mocking two-fingered salute.
"Fenrir!" she screamed, "Fenrir Greyback, don't you dare leave me like this! FENRIR!"
With a smirk, the werewolf walked off into the streets. It would be fun to see how she got herself out of this one.