Why not

A last full moon night shone brightly over the not-so-quiet streets of Sunnydale.
It was a perfectly normal day - the one or other random monster on the loose, Buffy busy staking it out with vampire fodder, and Oz the werewolf shaking madly at the cage in his prison at the school library.
"Oz, cut it out. You know the rods are too strong. Be a good doggie. Do I have to chain you again?" Willow tried to pacify her friend.
Maybe some higher powers were pissed about a werewolf being called doggie, maybe it was just a dumb accident, but in the same moment a small earthquake hit Sunnydale, and the cage door came askew. Oz threw his body against it, and he crashed through, blowing the door off its hinges. He landed before Willow who stared at him in wide-eyed panic.
"GRROOAWFF!" Oz said, which was probably Werwolfese for "Lunch!" Then he stroke out with his claw.
Willow could retreat in the last moment, but the claw ripped through all her clothes. She turned and ran. Oz quickly was behind her, and another blow launched at her was aimed as lousy as the one before. Willow tripped over the shreds of her garments that came in her way and fell down.
Oz went for the deadly blow when he got a nice view of Willows breasts that had jumped out of her torn bra.
"WOOF!?" Oz growled, and no Werewolfese dictionary was needed this time, as a big erection started to poke from his fur. Evidently, some of his animalic brain recognized his former mate.
In selfsame brain, some higher math went clicking. Eat? Fuck? Fuck, then eat? Eat, then...oh, clearly two nonabelian operations.

Willow squealed as Oz also ripped off her panties, carried her off into the cage (his territory) and pressed her to the floor. The smell of her womanhood excited him so much that he throw himself over her in 69 style and slobbered her clit and pussy with his rough tongue. Willow squirmed and pedalled but Oz was far too strong. She sighed and decided that she could as well enjoy her last minutes, closed her eyes, fantasized that it would be Oz-the-human who licked her into submission, and spread her legs wide. Soon her juices went flowing. "SLURP!" said Oz, maybe meaning "Aperetif!"
And then Willow came. Her mouth opened wide for an orgasmic cry, but Oz had other plans and gagged her with his humongous monster cock.
Willow was very keen-minded. She wanted to say "OK, you let me live and I don't bite off things you may need later. Deal?" but a) it was impossible to reason with a werewolf and b) all she managed to get out was "MPPPF! MHHH!" anyway.
She tried sign language but of course 69 meant Oz looked somewhere else.
Finally, she managed to get his attention somehow. Oz withdrew his penis gag and asked "WAFF?" (What the fuck do you want?)
"OK, you let me live and I don't bite off...eh...damn."
"GROAWF!!" (Of course, bitch, you had enough foreplay and want to fuck now! Stupid me!)

Quickly, Oz changed position and impaled Willow on his boner. She was completely filled, in depth and width. Then he began to pump with mighty thrusts. Willow clasped her legs around him to slow him down a bit. She felt another orgasm coming. Her vagina walls gripped Oz' dick like a vice. He let out a triumphant howl and squirted liters of werewolf cum into her. Seconds later, he fell down on her, snoring.
Some things never change.
Willow lie exasperated under him when she felt something was swelling in her vagina. It grew bigger and bigger, stretching her to the limits. Suddenly she remembered that wolves belonged to the canine family and had their own way for not letting the bitch get away. Oz had tied the knot with her.
Tediously, she rolled on top of Oz. She tried to get up, but the dick was stuck in her like it had been superglued.
The pressure and the knot thobbing with the rhythm of his pulse was enough to excite her anew. And his fur kept tickling her clit. Willow had another orgasm.
And so the night went through, Willow tormented by orgasm after orgasm, being unable to get away, the monster knot having also a monster duration.

Until the morning came and the werewolf reverted to human form. It was a bit too late, though, because Willow and Oz already had some very, very embarassing explaining to do...

The End