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                The Science of Mind Merging                
                    -by SchrodingerFu-                     
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                         Chapter 1                         
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Chapter 1
Author's note:  First and foremost, thank you for choosing this piece of literature of mine to read.  No writer is anything without their readers, and I would like to properly recognize this.
Second, while I have been working on this story for a while, it is far from perfect, and I recognize that.  Thus, I impart a task on you, the reader.  If you find anything that sounds off, from incorrect or boring descriptions to out-of-character behavior or awkward phrasing, please do not hesitate to tell me, through a comment or a private message.  You would be doing me a service in doing so.  You don't need to do any of this, but if you want to, thank you very much.
Third, the cover picture was made by Eternal-Equilibrium on dA.
Anyway, without further ado, onward to the story.
PROLOGUE
“Princess, I implore you...”
“No, you may not.”
“Princess, I am dying.  I... I must...”
“You must obey your princess.  You know that.”
“Please...”
“Death is as natural as life.  You were a wonderful pony in life, but all things must come to an end.  Everypony dies eventually, even us.”
“P... Please... Princess...”
CHAPTER 1
“Your room is just to the left, Miss Sparkle,”  The royal guard said, clad in the standard golden armor.
“Thank you, sir,”  Twilight Sparkle politely responded.
The guard took his leave while Twilight entered her room and made herself comfortable.  His pace was brisk, but not rushed.  He gave the impression that he was sure where he was going and why.
Twilight listened to his rhythmic, calculated hoofsteps on the stone floor until it was clear that he was gone.  She gave a relaxed sigh and examined her room.  It was quite lavish compared to her quaint and simple library.  Between the canopy bed, beautiful silk sheets, rich burgundy rug, and sizeable stained glass window depicting the banishing of the Windigoes when Equestria was born, the room could easily be mistaken for the quarters of one of the princesses.  If Twilight knew one thing about Canterlot, it was that style and grandeur were always top priority.
Twilight laid on the bed.  Despite the fact that she had spent her entire life at Canterlot Castle, it was rare for Twilight to see the beauty of the place;  she always had her head in a book or some pressing matter to attend to.  She had never walked around the castle just to see it.  She regretted this; whenever she described Canterlot, she couldn't say much except for the generic “It's beautiful”.
She turned her mind to a more important matter, the reason for her solitary trip:  Shining Armor and Princess Cadance were due to return from their honeymoon that day, and Twilight wanted to get to know her brother better.  She had become far too distant from him ever since she moved to Ponyville, and she thought she could rectify that by spending some quality time with him.
She glanced out a nearby window just long enough to notice two pegasi dressed in royal armor pulling a rather fancy looking chariot.  Much to her delight, attached to the back of the chariot was a large white banner, which read “JUST MARRIED” in large, intricate letters.  What perfect timing, she thought.
The two newlyweds hopped out of the chariot to be greeted by Princess Celestia.
“Good to have you two back,”  she said in her usual, comforting tone of voice.
Shining Armor bowed while Princess Cadance gave her a hug.
“Oh, and Shining Armor,”  she continued,  “you have a visitor waiting for you.”
He rose to his hooves.  “A visitor?”
Princess Celestia, still engaged in her hug, gracefully pointed a hoof to her left.  Naturally, Shining Armor's eyes followed the hoof straight to his little sister.
Twilight beamed,  “Hey, big bro!”
His eyebrows arched and his mouth formed a smile.  It was just the sort of eyebrow-mouth combination that could only be described as pleasant, but unwanted surprise.  “Twilight!  What are you doing here?”
“Well, I've been thinking, and I think we've grown too far apart,”  Twilight said,  “Remember when we were little?  When we were the best of friends?  We've grown too far apart, Shining, and I don't like it.  Remember when the changelings attacked?  I felt like I didn't even know you!”  There was a twinge of sadness in her voice.
“Oh, Twily...”
“So I'm going to stay here until I know you like the brother I know I knew!”  The twinge of sadness disappeared from her voice like a hipster hearing a classic hit song on the radio.
“Oh, uh, that's great, Twily, but...”  He was trying to go soft on his sister, but he couldn't find the right words to get rid of her while sparing her feelings.
“Is there a problem?”  Twilight dearly hoped there wasn't.
Shining Armor's voice suddenly and jarringly turned cold,  “The royal guard needs to set up a contingency plan in case the changelings attack again.  The fact that they tricked us all so easily is a clear sign that we need to step up our defensive measures here at the castle.”
Twilight was caught off guard.  She couldn't think of any words to say.
Celestia cut in, putting an end to the very long hug,  “Shining Armor, I would like to speak with you alone for a moment.”
He suspected that she wanted him to let Twilight stay.  He really didn't want that, but he could never turn down a direct order from the princess.  He gave a resigned sigh and said, “Yes, Your Majesty.”
The two of them walked off a distance and started talking.
Celestia got straight to the point,  “I'd like you to let Twilight stay with you.”
Shining Armor grimaced,  “I thought you might.”
“If I know one thing about friendship, it's that it should never go to waste.  You want to get to know your sister, don't you?”
“Yes, but I have more pressing matters to attend to right now.  Any other time would be fine, but-”
“She could help you, you know.”
“Forgive me, Your Majesty, but I disagree.  We've got a lot of work to do, and having to look after Twilight isn't going to help that.”
“I don't think you give your sister enough credit.  In times of stress, a pony's true self is revealed.  You could learn a lot about her, and she could learn plenty about you.”
“I don't think she'd like my true self very much.”
“She cares about you a lot.”
Shining Armor didn't speak.
“If I need to make it an order, I will.”  Celestia giggled the sort of giggle that you wouldn't expect to come from a princess, especially one as revered as Princess Celestia.
He sighed and smiled,  “Well, I guess I can't argue with that.”
“Well?  Can I stay?”  Twilight excitedly asked.
Shining Armor sighed,  “Yes, you can stay. But only-”
He couldn't finish speaking before Twilight leapt at him for a hug.  “Oh, thank you!”  He couldn't help but smile.
He continued, “But only for today.  Tomorrow you have to go.”
“That's all the time I need!”  Twilight said, squeezing her brother tighter.
He turned to Cadance, “I might be home a little late, honey.”
Cadance smiled,  “Oh, that's alright.  I understand.”  She leaned in and kissed him,  “Take as long as you need.”
Shining Armor turned back to his sister, “Alright, Twilight, let's go.  I've got a lot of work to do, and you're going to help.”
Twilight jumped to attention,  “Great!  I can't wait!”
With that, the two started their brisk walk to the local barracks.
The barracks was fairly mundane, despite being full of royal guards of all creeds and colors marching about.  Shining Armor showed Twilight Sparkle the various rooms and their functions: meeting rooms, tactical planning rooms, exercise rooms, and the cafeteria (which was serving a delightful little meatloaf dish which almost precisely resembled vomit in the right light, and cerberus excrement in the wrong light).  Along the way they were greeted with various shouts of “Hey, Shining Armor!”  and  “Good to have you back, boss!”  After a few hours, they arrived at Shining Armor's personal quarters.
“Well, Twilight, I've got some private work to do in here, if you don't mind.”  Shining Armor tried to retreat to inside his humble room.
“What kind of work?”  Twilight's curiosity knew no bounds.
“It's... private.  You wouldn't be interested.”
“C'mon, big bro.  We're family, right?  You can share anything with me.  Please?”  Twilight begged with her eyes as much as with her words.
He averted his gaze from hers and tried to escape inside his room again,  “No, Twilight.  Just go talk to Princess Celestia or something.”
“But she told you to let me come with you, didn't she?  Why can't I see what you're doing?  Maybe I could...”
Shining Armor cut her off,  “This is a private matter, Twilight!  Just go away!”  He slammed the door behind him, leaving Twilight Sparkle suddenly, bitterly alone.
She knocked on the door.  He didn't answer.
Twilight was thoroughly confused.  In their years together, he had never snapped at her before.  What could be so important that he would want to get rid of her?  The question baffled her.  He clearly wanted her gone, but why?
She put the question out of her mind.  She had always heeded her brother's advice, and that wasn't about to change.  She was going to talk to Princess Celestia to try to find out why he was suddenly so grumpy.  So off she went, bounding down the halls with unusual gusto, drawing plenty of attention from the guards in the barracks.  This attention mainly consisted of the occasional glance or sneer, and even a catcall or two.
From the corner of her eye, Twilight noticed the royal garden out the window.  For some reason she felt drawn to it.  She closed her eyes and focused on a nice patch of grass, shielded on three sides and on top by a number of large trees.  This spot was conveniently visible from the window.  With a glimmer of her horn and the flash and sparkle that usually comes with her magic, she was there.  She always felt a wisp of self-satisfaction when she successfully teleported.  Not many unicorns could, and she was proud to count herself among a gifted few.
The spot was surprisingly cool, despite the beating sun.  The ground was moist, but not too wet, and the air was crisp, but not too strong.  It felt like the perfect place to lie down, forget about your troubles, and just be happy.
Twilight curled up on the ground and shut her eyes.  She let out a deep, relaxed sigh.
Not a moment later, she heard a familiar voice.  “Hello, Twilight Sparkle.”  It was Princess Celestia.
Twilight jumped.  “Oh, hello, Princess.  I didn't see you there.”  She gave a quick, deep bow.
“Oh, no need for formalities, Twilight.”  Celestia let out a small grin.  “You know, I come to this same spot all the time just to sit and think.”
“I didn't know that.”  Twilight said.  Of all the places to go, what are the odds I picked this one, she thought.
“So, what brings you to the royal garden?”
Twilight sighed,  “Shining Armor got really upset about something and told me to leave him alone.”
“Oh?”
“I just want to bond with him, but he just wants to get rid of me.”  Twilight said.   She sounded more than a bit crestfallen.  “We've known and trusted each other for years, and now he won't even share his work with me.”
“If you really want to be closer to him, I could help.”  Celestia said encouragingly,  “There's a spell in the Star Swirl the Bearded wing of the library.  I think it could help you.”
“A spell?  What kind of spell?”
Celestia smiled,  “You'll find out.  All I'll say is, it will definitely help you understand how your brother is feeling.”
Twilight's eyes filled with excitement,  “Really?  That sounds perfect!  Thank you, Princess!”
Celestia smiled,  “Anything for my most faithful student.”
Twilight immediately started galloping to the library.  Celestia smiled again as she watched the excitement in her young pupil's eyes.
Twilight entered the Star Swirl the Bearded wing of the library.  It was unusually aligned, with a circle of bookshelves radiating from the centre of the room, as opposed to the standard ordered rows of shelves.  On the floor in the center of the room was a beautiful carving in the floor of the sun, the moon, and, oddly, no beards.  The plethora of books lining the shelves immediately excited Twilight, but what really caught her eye was the glass-covered exhibit at the end of the wing.  It was out of place for a library; it was more fitting to a museum.
She began the long walk down the cold stone floor.  When she arrived at the display, her eyes turned upward to a bronze plaque, which read, “The Final Project of Star Swirl the Bearded”.  Dozens of pieces of parchment sat in the display, all of them creased, worn, and yellowed to a dingy brown, leaving the words barely ledgible.  All sorts of notes and drawings were haphazardly scrawled on every page.  The notes were not so much notes as short phrases which didn't seem to relate to each other.  Twilight was a bit frustrated that she couldn't understand any of it.
The rightmost piece of parchment stood out, in that Twilight could actually make out what was written on it.  This was because the only words it bore were “TWILIGHT SPARKLE” in bold letters filling the entire page.
Twilight was caught off guard.  She certainly hadn't expected such a message, especially to her.  Was this what Princess Celestia was talking about?  She looked around.  There wasn't another pony to be seen.
The display case emitted a deep, slow creak as she opened it and carefully took the parchment.  On the back was another instruction, “CANTERLOT DUNGEONS, WING B, CELL 29.  PERFORM THE SPELL.  ALL WILL BE EXPLAINED,”  followed by a long incantation.
This last line piqued her curiosity.  Was it referring to Star Swirl's work?  Twilight had always known that Star Swirl the Bearded was often hailed as the greatest sorcerer of his era, perhaps the greatest of all time, and her heart raced at the prospect of his greatest work being unraveled to her.”
But, the Canterlot Dungeons hadn't been used in years...
...Right?

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                         Chapter 2                         
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Chapter 2
CHAPTER 2
Her curiosity had gotten the better of her.  Twilight held a lantern above her with her magic.  A copper plate on the left wall read “Wing B”.  The entire dungeon was devoid of any semblance of life, save for the damp floors, growing mold, and the occasional rat.
Twilight quietly counted the cells,  “...twenty-seven, twenty-eight, twenty-nine.”  She let out a terrified gasp.  In the back of the cell was a pony.  Twilight jumped back when she heard a sharp wheeze coming from him.  The pony's mane and tail hair was grey and sparse, matching its skin.  He didn't seem to notice her.
Twilight's curiosity suddenly struggled against her fear for her life.  Her eyes darted to either side.  There was still nopony around.  All she could hear was her own heavy breathing, periodically interrupted by the prisoner's.
Twilight Sparkle was confused.  Why would anypony be locked up down here?  Why would there be an instruction to go to the dungeons and perform some spell?  Twilight sighed.  The only way to know these things was to do the spell, and she knew it.
She tried to prepare her target in the cell,  “H-hello?”
He wheezed again.
“Can you hear me?”
No response, save for another strained wheeze.
She rolled her eyes,  “Well, that certainly helped.”
Twilight thought for a moment.  Could she be held responsible for her actions?  The instructions were there, was it her fault to follow them?  She couldn't know the exact nature of the spell until it was cast.
Regular, everyday unicorn magic was a simple matter of exercising one's will on the world around them.  Complex incantations like this were entirely different.  Words of power like these aren't invented, only discovered.  It's been said that the first magical incantation was discovered accidentally, in casual conversation, with destructive results.  The rest were found through random trial and error by eager unicorns, with further destructive results.
She closed her eyes and concentrated.  She steadied her breathing, and her horn began to glow.  She opened her eyes and whispered the incantation on the parchment.  Her horn glowed brighter.  She gazed at the other pony.  As the spell began to take effect, her breathing grew heavier.  The grey stone of the dungeon walls faded from her view.  All that she saw was the pony.  A million thoughts flew through her mind.  She tried to remember them, but she couldn't seem to focus on anything.  All she could do was look at the jailed pony.  His wheezing became louder and louder.  The sound was becoming unbearable.  She screamed in pain.
Twilight awoke in a great, pitch-black expanse.  It was entirely devoid of anything even resembling anything of any description.  It was just a big, black, empty, black space.  There wasn't even a floor or anything.  She just sort of hung in the air, if it could be called air, which it realistically could not.
A single wisp of light popped into existence just in front of her.  It danced all around her face before sitting motionless in the air.  Twilight oriented herself to face it just as it suddenly accelerated directly toward the center of her face.  She screamed out of pure surprise and, without warning, blacked out.
Twilight awoke with a start.  She had collapsed on the floor.  Her head was pounding.  The only thing on her mind was a surprisingly vivid image of Star Swirl the Bearded.  The grey pony in the cell was unchanged, still breathing in bursts and unaware of Twilight's presence.
She began her long trek out of the dungeon.  How long had she been unconscious?  Her brother might be looking for her.  Princess Celestia would certainly be worried if she was suddenly missing.
Suddenly, she heard something.  It sounded remarkably like somepony clearing their throat.  For the third time that day she looked around, and for the third time she found that she was entirely alone.
My name is Star Swirl the Bearded.
Twilight gasped.
You have successfully followed my instructions.  Your magic is indeed powerful if you were able to cast the Mind Merging spell.
“What's going on?”  Twilight said.  He didn't seem to hear her;  if he did, he didn't seem to care.
I had passed a part of my own mind on to him so that I could impart this message.  I wish to bring the knowledge of this spell to future generations, and so far you have been the first to use it.  Thus, I will explain the spell and its origins to you.
Before I continue, I should clarify what you are experiencing. I am simply a memory being accessed by your mind.  You extracted this memory from the stallion over there and brought it to your own mind.  This is the essence of Mind Merging.  You see, the mind is a wonderfully powerful, versatile thing.  I have discovered that it is possible to split your consciousness and be within the minds of others.  You can truly know them in a way infinitely superior to merely speaking to them.  You can experience a pony's entire life in seconds.  You can accumulate every piece of knowledge they have ever known with but a thought.  It is truly an amazing spell.  You should consider yourself lucky that you can utilize it properly.
Twilight was in awe.  Could this really be true?  Could she really do such a thing?  She could hardly comprehend it.  Her breathing quickened.
Mind Merging is quite a versatile spell.  By imparting some of your own consciousness to another pony, you could, for instance, communicate telepathically, read their thoughts, even influence their decisions.  In its fullest and most complete form, your mind will become one with the mind of your subject.  You will think, act, and live as a single mind commanding two different bodies.  Your exxperiences and memories will fuse, and two ponies will become one.
I'd like to share with you, a dream of mine.  I dream of a time when my Mind Merging spell becomes so popular that every mind has fully merged with every other mind.  I dream of a time when Equestria is under a single world consciousness.  There will be no arguments, no petty squabbles.  Everypony will be at peace, and we will all be happy.  After Equestria is united as one, we would expand.  Every hill, every vale, every forest and every valley would belong to us.  And within our grand, perfect mind would not be just ponies.  Every intelligent creature in all the lands would become one with us.  Ponies will wither and crumble, but they will never truly die, as their minds live on in beautiful harmony with us.  We will be the grandest, most powerful, and most intelligent kingdom that has ever been or ever will be.  And when we are finished, we will transcend the earth and soar above the clouds, into the great black abyss, and we will conquer it, and we will return, content in our infinite knowledge, and we will be finished.  Life itself will be complete.
Twilight couldn't help but feel a bit sad.  Star Swirl the Bearded lived over a thousand years ago.  It seemed he would never see his dream come to life.
You now know the truly wonderful power of the Mind Merging spell.  However, I wish to impart a warning.  When two minds are merged, even in the slightest form, it is impossible to separate them.  The two minds become too intertwined, too dependent on each other to ever be split apart.  I know this from experience.
The word lingered on Twilight's lips, “...experience?”
You see, I was the original test subject in mind merging.  Our minds became one, and my own physical body died almost immediately afterward.  I was devastated.  I no longer had a sense of self.  Everything that I did was through her.  I lacked an identity.
I always worked better at night...
Star Swirl let out a deep, world-weary sigh.  Twilight was suddenly overcome with feelings of guilt and despair.
I merged my own mind with the princess.  In my outrage, I seized control.  I used my power, and I used hers.  She couldn't stop me.  It is my fault that the princess was banished to the moon, and as a result I suffered the same fate.
I still reside in her mind to this day.
Twilight was speechless.  Star Swirl the Bearded was still alive!?  It seemed impossible.  Why had the princesses never mentioned anything?
Now you know the powers and the dangers of the Mind Merge.  Use it as you wish, but please do not make the same mistake that I did.
Star Swirl disappeared from Twilight's mind.  She wasn't quite sure if what had just happened was real.  Nevertheless, she had an answer to her dilemma.
Shining Armor sat alone in his room.  It was a standard room for military officials; simple grey stone walls, floor, and ceiling.  There were no windows, only a single small bed in the far corner.  He was hard at work filling out dozens of forms at his desk when he heard his thin wooden door creak open.  It was Twilight.
“Twilight, I told you I was busy.”
“Shining Armor, do you really care about me?”  She stepped inside the room and closed the door.
“Twilight, I've got work to...”
“Do you really care?”  She stepped closer.
He sighed,  “...Yes, of course.”
“Good,”  Twilight took a deep breath,  “I need you to trust me.”  Her horn lit up.
“Twilight, what are you doing!?”  He backed away from her.
She closed her eyes,  “Just trust me!  Close your eyes!”  Her horn glowed brighter, outshining the lantern.
He felt his head pounding,  “Twilight, stop that!”
“Just do it!!”
“No!  What's going on?”  His breathing quickened.
“You need to trust me!”
“But...”
Twilight opened her pleading eyes and looked at her brother, horn still shining,  “Do you trust me?”
For a moment he didn't respond.  Twilight's horn became brighter and more painful.  She let out a scream.  A tear streamed down her face,  “Please...”
Shining Armor's face fell from shock to sorrow.  He took a very deep breath and closed his eyes,  “Alright.”
“I trust you.”
Almost an entire second passed before the spell took its effect.
Almost an entire second later, Twilight Sparkle regretted casting it in the first place.