As she stood facing her twin, Twilight gasped. Then she asked “What are you?”
Her double replied “I am what you left behind. I represent what was taken from you, and I was given form by this realm that you now inhabit.”
Twilight thought about it for a moment then asked “How would you like to leave this place?” Her double (who is going to be called Sparkle for simplicity sake) replied “I would love to see the outside world.”
Twilight placed her hoof on her shoulder and said, “Girls, meet me back at the entrance.”
A voice sounded out from the ether “Okie dokie lokie” another sounded “Sure thing Twilight, This place is giving me the creeps.”
Twilight turned to her double and said “I’ll introduce you to my friends.”
Sparkle looked confused “Friends? Since when do you have friends?”
“I’ll explain on the way.
After explaining what happened to her ever since she left, Twilight got to the entrance of the “Library of Eternity”. She looked around and wondered, where are they? She placed her hoof on her shoulder again and asked “Where are you?”
Pinkies voice sounded “I think I’m lost. OOH, give me a second.” Several books were thrown off a nearby shelf and Pinkie extracted herself from behind where they used to be. Pinkie sighed with relief and said “I’m glad that works here.” Sparkles jaw dropped. “How…what….HUH????” Twilight giggled at the confusion of her double. “She’s one of the friends I told you about. Sparkle meet Pinkie Pie and Pinkie meet Sparkle.”
Pinkie jumped with Excitement at meeting who she believed to be Twilights twin sister. “HI!!!!”
Twilight then asked “Pinkie, have you seen Dash?”
“Not since we split up.”
Twilight then thought to ask “Have you gotten any strange feelings since we got in here?”
Pinkie replied “None that I can feel…” Pinkies tail twitched “...Uh Sparkle could you move 6 steps to your left.” Sparkle did so and just two seconds after she had left her previous location a Rainbow colored streak immediately hit the spot where she was sitting..
After explaining her double to both Pinkie and Rainbow they decided to leave the Library for a while. After stepping through the portal back into the Ponyville library Twilight looked at a clock hanging nearby and discovered that they had only been inside the library for 10 seconds. Then Twilight decided to ask, “Did you find any Daring Doo books, Rainbow?”
Rainbow answered “All 45 books.”
Twilight was intrigued, but said “Don’t spoil it for me. I’ll read them when they come out.”
Twilight then spent the next few hours Introducing Sparkle to the rest of her friends. Fluttershy was confused at first but eventually came around to accepting her. Rarity was fascinated and smothered them with ideas about matching dresses and even color matched opposite designs. Applejack was all confused, both before and after the explanation.
After sending a letter to Princess Celestia explaining that she had found something interesting in the Library realm, she realized how late it had gotten and told Sparkle that she was going to sleep and advised her to do the same. Sparkle agreed to use the guest room.

Twilight rolled around in her bed for the next hour trying to get to sleep. She was about the drift off to sleep when she felt a presence. “Spike, is that you?” She asked, getting no response. She lit up her horn with a light spell shooting beams of light into the darkness. She looked over at Spike and saw a glow surrounding his body, mainly his head. She made to get out of bed, but found herself pushed back down onto the mattress as she was overpowered by a magical field. She struggled against the bonds to free herself, but stopped when she heard a voice. “Oh dear Twilight, The time has come.” She looked around and saw Sparkle walking out of the shadows and into the light, Sparkle climbed on top of the bed with Twilight and straddled her body, “The time has come for us to become one again.” She leaned her head down to Twilights face. Twilight turned her head away from her double, who quickly forced it back into place with a quick burst of magic. “Don’t worry so much, it’s not good for you.” Sparkle then kissed Twilight full on the lips, Twilight tried to scream but found her mouth occupied by Sparkles tongue as it explored her mouth. Sparkle reached her fore-hoof down between Twilights thighs and started to rub her sensitive spot. Twilight moaned slightly as the hoof message her, but continued her futile struggle against the bonds holding her in place.

Twilight began to feel a sensation growing, and she involuntarily bucked her hips against Sparkles hoof, “It looks like someone is enjoying herself.” Twilight’s moans became louder and louder as the sensations grew, eventually peaking and she felt her whole body tense up and juices sprayed from her nether region. Sparkle brought her hoof back up and licked the juices off of it, “You’re quite the tasty one. Now that you’re more receptive, we can become one.” Sparkle touched the tip of her horn to Twilights and they both started to glow slightly. Sparkles body became more and more translucent and eventually became transparent as she transferred her essence into Twilight, who became consumed by a growing hunger.

At this point Sparkle was fully absorbed by Twilight, who got out of her bed. Now that she was free of her bonds, she started thrashing around in her room with her fore-hooves grasping her head. The pain coursing through her head was unimaginable. Suddenly the pain peaked and she screamed out at the top of the lungs. She then collapsed into a pile in her room, breathing heavily. Eventually she got back up, with a smirk on her face. “Let’s have some fun. I need to get my tools ready.” She went down to her “secret” lab down in her basement and started gathering up knives, tools, surgical equipment and various chemicals. She put all of this into a saddlebag and walked out of the basement, out of the Library and into the darkness. “Let’s pay Rainbow a visit.” She walked over to Rainbows house on the outskirts of town.

Twilight looked up at Rainbow’s house with a sneer on her face. She Cast the Cloud-walker spell onto herself and teleported up into Rainbow’s house. It appeared rather Spartan, despite being so extravagant from the outside. She found her way to Rainbow’s room, quietly opened the door and walked in. She saw Rainbow sleeping quietly on her bed, cuddling with a Lyra Heartstrings Plushie. That’s odd. Twilight thought. Twilight used her magic to move Rainbows body into a spread eagle position and used various spells and enchantments to keep Rainbow restrained in said position. Twilight then placed a black-magic enchantment over Rainbow body to keep her alive as long as possible even after what should be fatal injuries. Twilight then cast a sound-proofing spell onto the room and used a voice enhancement spell to simulate the Royal Canterlot voice. “WAKE UP RAINBOW!!!!!” Rainbow didn’t stir despite probably having gone deaf, Twilight face-hoofed at her rock of a friend. “I didn’t know Tom was a changeling.” Rainbow stirred awake, “Oh sure, you don’t wake up at me shouting, but you wake up at a whisper.”
Rainbow asked “Twilight? Why are you here and why can’t I move?”
Twilight looked at her friend and said, “We’re going to have a bit of alone time.” as she raised a knife into Rainbow’s sight, who immediately tried struggling against the Spells holding her in place.
“Twilight, jokes over. Can you please let me go?”
Twilight brought the knife down and rubbed Rainbows check with it. “And ruin the fun? I don’t think so.”
Rainbow gulped and asked “What are you going to do with me? Turn me into Cupcakes?” Twilight Laughed and replied “Nothing so cheesy. I’m simply going to cut and gut.”

Rainbows eyes nearly popped out of her head. She began screaming for help. Twilight reached into her Saddlebag and Brought out a hacksaw. “First, your wings.” Rainbow tensed up as she felt the coldness of the blade touch her wing. Twilight began slowly moving the blade back and forth along Rainbow’s flesh cutting through it, Rainbow was screaming loudly in pain as the blade began cutting through the bone. The pain pushing its way through her mind was overwhelming. Twilight sighed contentedly as the blade fully cut through the wing. She removed it from the bed and placed it into a pocket dimension she had formed just for this purpose. Rainbow was crying partly at the pain of losing a wing and partly at the betrayal of her friend. Twilight began cutting through the other wing, drawing blood and screams. She cut her way through and placed it into the pocket dimension. “Oh I almost forgot.” She conjured a flame spell to cauterize the stumps. Twilight put the hack saw back into the saddlebag and thought “Why didn’t I create a pocket dimension to hold my tools? I’ll have to do that later.”

She removed a scalpel from her bag, placed it against Rainbows Cutie mark and began to cut it off. Rainbow was once again screaming in pain as more of it was cut from her body. Twilight moved to the other side and cut off the other one too. She placed both bits of flesh into the pocket dimension after preserving them with magic. Twilight looked at her friend, “I’m not done. In fact, I’m just getting started.”

Author's Note

editing suggestions by Mithos_Yggdrassil. (thanks)
sorry about the dramatic shift in style. it was at his suggestion.