Archive of Our Own

Isabela didn't know what was wrong with her. It started out innocent enough, a sudden craving for meat here, a lingering gaze at a neck there. But it transformed, slowly and subtly like a poison running through her veins.

Isabela was perfect. That meant the nightly shivers and sudden cravings, didn't exist outside the safety of her room. The cravings were the worst, and always for the wrong person. She couldn't help it, "It's not my fault, I swear it's not my fault. God... why did you do this so me." Were nightly phrases from her.

Mirabel. 'Oh Mira... I'm so sorry, it's not my fault... not my fault.'
The images never stop, blood and cum all mix together in her mind. Fucking her precious little sister while ripping off parts of her to chew and swallow. The moans of ecstasy, of pain and horror, all fuel for Isabela, fuel for her vines to knot inside of her, thrusting so hard and so fast she sees stars. Every time she gets overwhelmed with this feeling, her body reacts. The popping of muscles and bone, the loss of finger nails and teeth only for it all to grow back anew, but different. Sharp and long. She can feel her body on fire as the pain of her skin ripping and her vomiting up organs only to grow back monstrous, morphs into a raging pleasure.

The thought of mirabel moaning under her as she fucks her with all sorts of plants and vines, stretching her as more and more bloom within her enlarging her stomach. The thought of her claws and teeth ripping and tearing until her flesh is done. Mutilated just to be eaten and savered as she cries and cries. Mostly in pleasure, but pain is a strong trigger.

It took Isabela many years of fighting her emotions, of turning her burning desire to bite and fuck into the actions of teasing and scorn. She knows she's disgusting, mirabel was a small child when it all started after all, but as long as she doesn't show it, as long as her lingering gazes of hunger are interpreted as annoyance then she's fine.

While Isabela is disgusted and fearful, she's also prideful and bold. When her fear is worn down by arousal and fatigue, she feels proud of her strength, of the way her new form can leap from the large branches she grows. The feeling of being free, of being not quite the perfect Isabela, but the monster she is now, is the best thing she's felt in years.

However, all things must come to a standstill. Tightly coiled muscles wait in utter stillness, perfectly hidden in thick foliage, as a specific scent spreads out all around her. She can feel the cock of this form rip from its hood and grow as she hears the calls of, "Isaaa! Are you in here?"

Poor little Mirabel who was kind and loving, always ready to help the family. Now the subject of slitted pupils in acid yellow eyes. She shuts the door, searching the room as she calls out some more.

The beast who is hungry and prideful, not to be denied by its desired mate. Lunges at its youthful little sister, pinning her to the ground as her claws sink slightly into her shoulders. Hips press down onto the thin material of her skirt.

Mirabel screams, oh how she screams before suddenly, it comes to an abrupt stop. "I-Isa?" Her face is one of shock and fear, slowly morphing into realization and Intrigue. "Is that really you..?" The only confirmation she gets is a quick lick on her face before she yelps as her shirt and skirt are ripped off. She bearly has time to scream as a thick dripping cock is forcing its way into her. She struggles, she screams, but it only makes her sister want her more.

It takes a bit, around ten minutes of groaning and painful yelps from mirabel before the pain weavers, then morphs into the sinking feeling of pleasure. Unwanted pleasure as her own sister pushes into her, panting and lapping at her neck while completely dwarfing her in size. Little by little she starts thrusting back, scratching down her sisters back and bearing her neck for it to be licked.

Isabela was in heaven. Her precious little sister was under her moaning her name while she fucks her. She knows it's not enough though, so she wills vines to take root in her sister's ass as they slowly enlarge and creep out of her, only to thrust and push around inside of her. The sounds of her little mate moaning in pain from her assfucking makes her thrust harder and faster. Every so slowly squizing her knot past that stubborn ring of muscle of her pussy.

Isabela knew what she had to do. Ripping down her mates shoulders as she picks her pick, letting gravity help her in slamming in her knot. Using the adrenaline of her little sisters screams to bite at her neck, sinking her fangs into her soft delicious flesh. Marking her with the same beast as her own, condemning her to a fate of great humiliation and freedom.

With brief clarity, Isabela delicately lowers her bonded mate, careful not to jerk her cock to much as it fills mirabel more and more, until her already pudgy stomach is bloated and swelling. She curls up around her sisters much smaller form. Waiting for the gushing blood to stop, for the wounds to close as mirabel wakes up no longer quite as human.

Isabela was born with this horrible blessing, but Mirabel is now infected. Swelling with kids she won't be able to explain, forever tied to her own monstrous sister, now a monster herself.