“Hey! What about this one?” Derpy called from an obscure corner of the stuffy library.
Flying over, she held a simple, brown-covered book with a generic black Earth pony silhouette on it. We cracked open the book to the title page…
“Crystal Fist: The Being Between Dimensions, by Tangerine Hopes,” Derpy read.
“Celestia didn’t have this book in Canterlot,” I recalled.
I decided one more before a break wouldn’t hurt. We flipped open the book. The first chapter was obviously written from before her descent into madness. It detailed Tangerine’s tales into a village of Dimensians, a race given the extraordinary task of keeping the fabric of dimensions properly spaced. It suggested a measurement of less than two-thirds of a nanometer each for the Five Walls separating completely disconnected worlds, and even smaller to absent measurements for specific walls within those that were media-connected.
The second chapter detailed her first meeting with the Dimensian princess Crystal Fist, the perfect duplicate to Princess Celestia between the dimensions, albeit with a few more psychotic tendencies like a desire to force takeover of others’ bodies. She swapped forms twice during her visit, but called it a “psychological disorder” and convinced Tangerine she was of no threat.
The third chapter dealt with the physiology of Dimensians, differentiating them from Changelings, but with the realization that they were at one point a singular race with both powers that had optimized itself over time into two. The evidence was in the absence of a horn for Dimensians.
The next several chapters detailed in Twilight-esque great lengths how Tangerine’s psychology was slowly, delicately, and carefully disassembled by her host, even as she was enthralled with the spectacle and grandeur of the Princess. All the while, Tangerine kept her denial of the events up, though, by the timeline given by her other books, she also continued to chronicle all her other adventures. She attended several festivals, documenting three Equestrian years in the village by marking each birth date with a party in her honour, but passing over hundreds of thousands of years of world history in about ten thousand words.
The tenth chapter was blank, except for four lines.
“She’s in my brain… The life inside is breaking up…”
A gnawing at the back of my mind left me unable to focus enough to read the last two. Derpy looked at me, concerned.
“Are you okay, Zytharros?” she asked.
I walked in circles for a little bit, collecting my temporarily-shattered mind. The headache passed.
I gave a concerned glance at the soft, gray mare, frowning in thought. “I… I don’t know for sure… I think I’m fine… for now…”
Derpy nodded nervously. “Okay. Remember, I’m here to help.”
She may be the only thing to keep you sane, a voice suddenly spoke, erupting into my head. It faded away into oblivion. My eyes registered shock. Derpy shied back a little at the sudden change in demeanor.
She was in my mind. Her seed was sown.
I needed to know something, and it was a need to know now, not later. I frowned and looked at Derpy. “Will you stand by me and even kill me if it is to save Equestria?”
“I-” she started. She was stunned.
“I need an answer,” I demanded, slight panic showing in my voice. “I’m sorry to put this on you, but if I lose it, I don’t want you knowing me as your enemy… ever. Will you kill me if I lose my mind?”
I shed a couple tears as I felt… something… creeping around in my mind. I knew I would not make it sanely… this time… without Derpy, though to which end of insanity I would go was still up in the air. She still hesitated, absolutely refusing to believe what she was hearing.
I sighed. “Derpy, just now, Crystal Fist came to me in my mind. She left behind a shard of herself that will slowly deteriorate my control. I need your help to rescue our friends, but I also need to know if you can carry the burden alone if necessary. One of those burdens, as morbid as it may be, may be finishing me off.”
Derpy swallowed. She scrunched her mouth, trying to decide whether to run or not. I could see her wavering as a front hoof steadily rose up, her one good eye racing around, trying to make a decision she had never made before.
Eventually, though, she settled her hoof on the ground.
She acknowledged her fear. “I don’t want to lose you like that…” she said solemnly. “But if I have to, I will.”
I pointed a hoof at her. “Pinkie promise.”
Derpy swallowed again. She tried to raise a hoof to complete the promise, but slowly lowered the hoof to the earth in shame.
“I… I can’t do it…” Derpy admitted quietly, a tear leaking from her bad eye. “I won’t. I won’t kill.”