These lithe, broken, mysterious creatures are worlds different from the hulking beasts that inspired their design, and everything from the way their armor appeared to how they cocked their head had to tell the story of their creation
The transition from a Little Sister to a Big Sister was never a pleasant one to witness. To see such a pure and innocent child turn into something that wouldn't hesitate to kill the very splicers she harvested. Splicers saw them as both little sisters and something else, but to them they were still a means to an end. So many things had happened in Rapture, but innocence's illusion destroyed was saddening. To those who still possessed emotions, that was. To most splicers they were still the ADAM gatherers they used to be, only they presented a challenge harder than the Big Daddy's that could easily be ganged up upon.
It started with their dresses becoming too small while they became too large and gangling for their old clothes. The already frayed seams constricting around their mottled grey flesh, their inability to maneuver around the vents. Their refusal to play with toys, how they admired the Big Sisters that escorted them around Rapture more than they ever did before. Sometimes, one would giggle with thoughts of getting a pretty dress of their own one day, or imitate the shrieks that signaled their coming.
Once they outgrew their mental conditioning, they were no longer classed as a Little Sister. No longer did they see the murderous inhabitants of the city as happy party goers, nor their silent protectors as knights in shining armour. The rooms were no longer filled with beautiful furniture with soft music coming from the walls, and there were no angels.
For the Big Sisters, it was an instinct to help the older Little Sisters who were soon to become what they were. At that age, there was nothing that could save them, that could make them be normal children once more. The Little Sisters were the only things that the Big Sisters felt anything for, but the only thing that they could do was to gather the scraps of metal that were to become the Sister's mock Big Daddy armour.
What was once fun, walking around Rapture with Daddy, turned into horror. All the more frequently while harvesting they would see Rapture for what it truly was, a decrepit city with drug-addicted, psychopathic inhabitants. Along with the vast amounts of consumed ADAM, such sudden sights made the Sisters even more unstable, and upon hitting the age that would have signalled puberty, they broke. Now as mentally broken young women, they were tasked with both the goals of their original protectors and their duties as a Little Sister. Although unable to produce ADAM, they could still harvest it.
The residents of Rapture grew to fear them. The screams of anger as a group of Splicers cornered one of these helpless children let them know that there was no escape. Like the Big Daddy's, only death would stop them from hunting down the ones who dared to harm the Little Sisters.
But as they would lie alone in a cold and damp room, helmet off and facing a dirty puddle of water, they saw themselves for who they really were. Monsters. Creatures that all feared. The once cute ADAM producers. But that was all they were as children: factories for people's expensive tastes to be used and cast aside for another day. It kept the fiery rage burning inside of them, the thought that one day they could have their revenge against those who twisted them in such unspeakable ways.
When a child was stolen, taken away and seemingly erased from all of Rapture, the Big Sisters knew better than to think a mere Splicer was able to evade them. The one who caused all of this; the downfall of Rapture and the process of becoming a Little Sister, the one who coined the idea of making a child ingest one of the repulsive sea slugs: Tenenbaum.
And deep down inside them, amongst the hatred in their minds, there was envy. Envy that these children were able to escape before it was too late. Envy that they wouldn't have to fend for others like them until death. Until they were useless.
I haven't written fanfiction in quite a while that didn't relate to very stupid themes, so writing something that didn't include making fun of stereotypical fics was both fun and slightly challenging. I'm hoping this opens a way towards not having writers block every few days, and real stories that I can publish and feel proud of.
As for the canonical part of this story, it was never intended to be a continuous fanfiction and it never will be, it's just a one-shot that I thought up a while ago. If I were to find something that was really out of place in the story compared to canon I would change that.