By necessity, the nature of ascent to and abdication from the Crystal Throne was determined neither by right of birth, nor by personal power, but rather by the sheer volume of Love an individual pony felt. This was a rather unfortunate necessity, because Love, while unspeakably powerful, was typically fleeting and had a strong tendency to woefully exhaust anypony who expressed it in great amounts. Love was, after all, just as demanding as it was giving, and those ponies who gave too much or had it stolen from them by the wicked Changelings were left empty husks barely clinging to life.
Thus it was that whenever a given pony petitioned for seat upon the Throne, it was typically rejected or accepted immediately, because either they had enough Love to notice upon their entry to any building, or they didn't have enough to reign. Of course, just to be sure, there was still rigorous testing to make certain that a pony had the durability to sustain that Love when it was needed most: when none but the reigning Emperor or Empress had the energy or will to power the Crystal Heart, the ponies of the Empire would rely solely him or her to protect them all.
The unicorn known as Sombra Soul was no exception. He wanted the throne, not because he wanted the power and authority it bestowed, but because he loved the Crystal Empire itself. Growing up, the ponies around him had made him feel welcome in spite of the bizarre deformity that was his generally bleak appearance and demeanor. He was as loved as Princess Luna and much more aware of it than she was.
As it happened, the source of Sombra's grim disposition was that he was absolutely terrified of the dark. So much so, in fact, that he could not sleep unless he was in a room so suffused with light that nothing in it could produce a shadow. That, combined with the fact that his magic aura was black, filled his heart with a steady stream of misery which was only assuaged by the efforts the Empress and her citizens put into making him and each other happy. After all, what greater source of joy can there be than knowing that somepony wants you to be happy? So it was that he made to the residing Empress, himself, and everypony present at the coronation a solemn vow that he would do everything in his power to keep the flame of the Crystal Empire's beneficence alive with all his heart:
"My dear mares and gentlecolts, I cannot begin to tell you how pleased I am to have this opportunity to serve as your Emperor. I... honestly, my heart feels as though it is about to burst with joy. I love you all, and I mean that with the utmost sincerity. The kindness you have shown me as a colt is one that I have always felt could not be compensated with meager words alone. And that warmth, my dear little ponies, is what has driven me to here, where I stand before you today. I take this Crystal Crown as the only means I can dream of by which I can return to you the incredible Love you have given me throughout the course of my life. My Empress? I stand ready to face your judgment!"
The throne room erupted in a roar of cheer that resonated off its crystal walls, and below the Palace, the Heart flared brilliantly with the surge of Love from the populace. Queen Crystalline was almost two thousand years old, and thanks to the taxing upkeep of the Crystal Heart, certainly looked it in spite of being an alicorn. Still, she stood with strength and regality enough to inspire the other two of her kind in the throne room: the Princesses Celestia and Luna, who had of course been invited to this and every previous coronation.
It was just as well, since nothing short of the presence of the Crystal Empress could tear the Princesses' eyes away from the young king-to-be. Not that Crystalline blamed them. Her petitioner was like a stallion out of a romance: tall, dark, handsome, brilliant, and full of sufficient Love to be felt over the "noise" of the crowd, just like she'd intended for him to. Of course, she blamed them anyway. If these two upstart little strumpets thought they were going to just swoop in and snatch up the Dark Prince she'd been cultivating over the past couple decades, they were in for a wholly unpleasant education. But for now, there was the matter of abdicating her throne with the dignity and grace befitting her years on it. Naturally, it helped that there was a certain test involved in the passage of authority, one which Crystalline was sure the Princesses would respond to in a manner that would seal them out of Sombra's heart forever.
( After all, if there was one thing that inspired hate in a stallion above all others, it was the sight of mares laughing at their insecurities.)
"Dearest Sombra Soul. Over the years, I have watched you grow into a fine and strong stallion. You have been by no means perfect, but you have worked harder than any pony I've seen in generations. Including your father, whom I must assure you would have been proud beyond words at the sight of you today, even if here wasn't where your journey had led you."
(Those silly fillies might believe otherwise, my colt. But you're mine.)
Sombra literally glowed from the praise, and Crystalline smiled.
"As is tradition, you have proven yourself to be more full of Love than any pony in the entire Crystal Empire. Better still, your stamina is second to none and the Light of your soul seems like to ignite the darkest of hearts and show them what they've been missing."
(You're mine!) Crystalline giggled.
"I can't help but feel your mother misnamed you. Oh! My apologies, darling. That was insensitive," she said, but her eyes had broken his gaze as a frown flickered onto and back off of his face. She was subtly glaring at the Princesses.
(MINE! ALL MINE! Mine. Mine! MINE! MINE! MINE!)
"In fact, that brings me to my next point. In spite of the losses you suffered, rather than growing cold and bitter, your heart only grew in strength. Independent and brave, in addition to being as strong as a draft horse and wise beyond your years, I have every confidence in the brilliant future you have to offer the subjects of our beloved Empire. However, you still must be witnessed enduring The Test before all who would come to recognize you as King. Are you-"
Suddenly, Crystalline used her magic to close the heavy drapes on the sunlit side of the throne room. Due to the natural light being the primary source, it darkened considerably. There was a chorus of gasps from all but the royalty present. Celestia simply ignited her horn with her soft, pleasant yellow aura. Luna could see equally well in all light settings, and sometimes didn't even notice the changes. Crystalline was expecting the difference. Sombra, on the other hoof, was paralyzed with fright. It was a requirement of The Test that the examinee was taken entirely by surprise by the presentation of their most deep-seated fears, to show beyond any shadow of doubt that they were capable. Though she would never admit it, she still harbored doubts. After all, the darkness conjured frightful hallucinations in the minds of many ponies, but none more so than those who were forced to admit their fear of it.
Rather than keenly observing Sombra, as she was supposed to, Crystalline again periodically looked over at the Princesses, who had held their tongues in the face of his public humiliation even better than the imperial citizenry, who were nervously whispering amongst themselves.
(They seem to have matured considerably since their last visit.) the empress thought, remembering how their own fearful reactions had only recently evolved into barely-stifled giggles over the course of their previous Tests. Now, they were silent. Contemplative. Respectful. (That is... not good.)
She was broken from her reverie by the throne room suddenly plunging even deeper into darkness, before all of that was drawn toward the position where Sombra Soul was standing, condensing toward his horn until it was strained back into his already dark mane, causing it to erupt in a manner not unlike those of the Princesses and Empress Crystalline herself. The throne room was filled with an eerie glow that seemed to be the absence of darkness more than proper light. Seeing him conquer his fears and subdue them in this manner, the Empress, and indeed every pony present, felt inspired to welling tears. He was glorious, and so was he loved. Rendered unable to speak, Crystalline returned Sombra's deep bow and used her magic to lift the tapestries and the Crystal Crown as one, allowing the returning light to reflect off the beautiful artifact as it passed from her aura into his. She stepped down as he stepped up, both careful to maintain a proper dress passage, then as he lowered the crown onto his head, the retired Empress led the assembly in cheering.
"All hail to your new Emperor, Sombra Soul!"
"ALL HAIL! HAIL TO THE EMPEROR! HAIL EMPEROR SOMBRA!"
Then it was Sombra's turn.
"All hail the Crystal Empire!"
"ALL HAIL! ALL HAIL! HAIL TO THE CRYSTAL EMPIRE!"
"Long live Emperor Sombra!" Crystalline led again.
"LONG LIVE! LONG LIVE EMPEROR SOMBRA!"
"Long live the Crystal Empire!" Sombra again.
"LONG LIVE! LONG LIVE! LONG LIVE THE CRYSTAL EMPIRE!" the crowd shouted back, before cheering and stomping their hooves so loudly that if there was anypony not caught up in the moment, they would have been deeply concerned with the structural integrity of the Palace. Far below, the Crystal Heart relayed such an abundance of Love that the borders of the Crystal Empire expanded by more than half their previous diameter.
As the cheering died down, Celestia cautiously tipped her head closer to Luna's, her face all sunshine and rainbows. She hoped that she moved close enough to be heard as she whispered to her sotto voce.
"I don't know about you, but I can't wait until the after-party!" she said with a playful wink.
"Um... Mm-hmm!" Luna responded uncertainly, quickly turning her face away from her sister for fear of the elder somehow reading her mind and finding out just what kind of "after-party" she'd been thinking about all day.
Then the newly-crowned Emperor smiled at the two of them, eliciting from both flushed cheeks, cleared throats, and awkward hoof scrapes as he approached. They noticed each other performing those actions, and in an instant, their rivalry sprang back into life. Even while they inwardly chastised themselves for falling to such a "petty" difference, neither of them would back down. But the Sisters' relationship had weathered quite a lot. Surely a stallion wouldn't be the wedge that fully divides them...
Queen Crystalline didn't especially hate the Two Sisters, but she was determined to see her strongest potential competition canned before they had a chance to present a real threat. Thus it was that between the coronation proper and the Shimmering Starlit Serenada (a high-class karaoke party), the former ruler of the Crystal Empire had made a quick little trip into the Forbidden Arts section of the Imperial Library. Therein, she browsed fervently until she found the book she was looking for: "Love Me Not", a book that was full of love-cancellation spells with the primary purpose of countering wayward love spells such as "Want It, Need It"; love poisons of varying flavors (no pun intended); and of course freeing the unfortunate from the shackles of unrequited or unwanted love so that the pony suffering from them could get on with their daily lives. It was an old tome, scribed in glyphs rather than words, and more etched than written into the layered-papyrus pages by the grand vizier of an ancient pony pharaoh.
Of course, Crystalline's intentions were not so benign. It took longer than she'd have liked to find the spells she was looking for, but she was a quick study and had them memorized in moments. As she prepared to cast them, the vizier's spirit appeared directly in front of her, which gave her quite a fright. Not least because she recognized him! He didn't look much older than when she'd seen him last, and that was quite sad, because he'd been in his prime. To her credit, she didn't condemn herself by screaming for the guards, who of course would have been immensely curious as to why she was summoning ghosts from the pages of lore she herself had rendered taboo. Instead, she smiled at him and spoke coyly, as though she meant to seduce him.
Not that she had any reason to doubt her ability to, had he been alive. Taking aside the fact that she was still an alicorn specialized in Love magic, the millennia had done little but refine her beautiful appearance. Standing taller than nearly anypony, her coat was the shining black of polished obsidian and her mane and tail descended from her like ever-flowing cascades of liquid emerald. Her exquisite wings scattered any focused light that struck them in a dazzling display of every shade of green a pony could conceive of, and probably several they couldn't. Her horn, rather than the primitive, twisted lances of her "lesser" southern cousins, was a curved dark blade akin to her fellow Shadow Crystal Ponies, including Sombra's (though his was inexplicably red).
"My, my..." Crystalline purred, her voice the product of natural talent honed by centuries of practice. "Are you not quite the handsome spirit, Sire-"
"Do not speak my name!" The ghost hissed, his burning gaze and chilling voice sending shivers of terror through her in spite of her immense concern with maintaining her dignity. "The only possible reason I could be here right now is because some moron tried to cast the spells I bound my very being to the guardianship of! You cannot imagine my outrage and disappointment that you, of all ponies would be that moron, Crystalline!"
"Temper, temper..." Crystalline muttered as she rolled her eyes. "I am not going to cause any real harm. I just need to stop a couple of fool fillies from drawing both our nation-states into a boiling muck of unnecessary drama."
"You are going to cause far more damage than you can possibly imagine, Crystalline! Those spells you cast could doom our entire world!"
"Oh hush! Really now, there is no need to be so melodramatic! You act like an adolescent girl sometimes!"
"If that is how you are going to act over this dire matter, then so be it. Just know that you are not as powerful as you think you are, and that a curse cuts also its master, and none more so than a Love curse" the stallion concluded petulantly before vanishing in a puff of smoke. He wasn't going to fight because he knew both that he couldn't defeat her, and also that she already knew what she was doing was wrong.
"Like I said... melodramatic," Crystalline sighed as she began casting the spells. "First, for the younger will be 'The Eye of Chastity'. With this, she will be unable to perceive Love being directed toward her for... let us say about ten years. That should be long enough for even Sombra to give up on her."
She closed her eyes and focused on a mental image of the lunar princess's face, and after a flash of brilliant green light, she opened them again. After a couple minutes, she realized that she was breathing far too heavily. But she couldn't help it. She felt so... empty somehow. Hollow even. However, with some effort she got herself back under control.
"Now for the elder one... let us see. She is clearly the more proactive of the two, so she will require a different means of deterrent." She flipped through the pages some more until she alit upon inspiration. "Ah! Yes, this will do! 'The Stalker's Shame' will see to it that she does her best not to be too intrusive with her presence! It is brilliant! I do not see a duration on it, however. Well enough, it should at least be able to last the night, and that is all I desire of it!"
Another few moments with eyes closed and another flash of green light later, and Queen Crystalline re-shelved the book, wondering if she had started to lose her hearing or if the Imperial Choir had lost their key. Probably the latter. After all, her hearing was still quite sharp. So much so that she was able to hear how strangely hollow her hoofsteps sounded against the library's crystal floor. She paused on her trip back through the public aisles and lifted a front hoof to study it curiously, noting that though it didn't appear as hollow as it sounded, her coat had mysteriously lost its luster. The ghost's warning flashed through her mind, but she shook it back out. In its place were new concerns, primarily revolving around the effects that aging seemed to suddenly be having on her.
Like how her teeth itched, or how she felt with growing alarm a distinct stillness deep inside her chest.