It began upon Twilight's return from Canterlot. The swell of triumph from rescuing the Crystal Empire had faded over days of pleasant but routine life in Ponyville. However, the curiosity piqued by the possibilities of shadow magic had not.
Twilight's research into the dark powers soon stalled, as she had next to nothing on the subject in her little village library. Celestia has been hesitant to give her more on the subject, doing so only after Twilight promised to keep her work in such matters limited to the purely theoretical. For a few weeks, she did, but it wasn't enough. Questions were raised more often than they were answered, and soon the only way to solve the countless mysteries bouncing around the unicorn's mind was a practical experiment.
That brought Twilight to tonight, standing in her basement and running through her pre-ritual checklist. The moon was new. The runes were drawn in powdered onyx. The mana patterns of the spell were etched in her memory. Spike was at Rarity's.
Satisfied, Twilight took a deep breath, then called upon the powers of wrath and terror. Shadows spilled from her eyes and horn, burning and stinging as they writhed out of her aura. Darkness flowed out of the ancient sigils, quickly overwhelming the feeble glow of the firefly lanterns and shrouding the cellar in darkness.
Then, impossibly, it grew darker still, an eye-sucking void on the other side of night that nothing could hope to illuminate. The burn in Twilight's head gave way to a chill throughout her body, a cold that went beyond simple temperature and made her very soul shiver. As she struggled for breath, a low buzzing filled her ears and a terrible presence pressed down on her spine.
Numbness crept through Twilight's hooves as the void sapped joy and hope from her mind. Shadows from beyond death reached out for the cooling morsel that had so foolishly presented itself, eager to feed on her sweet dreams and ideals, on the rare treat of skin and meat and marrow. But first, first would be her color, the bright vibrant hue that spoke of light and life, of all they could not have, but would take and take until—
"ENOUGH!"
The darkness imploded, collecting into the exact center of the rough circle formed by the runes. Shuddering and gasping for breath, Twilight stumbled to her feet, feeling weak as a kitten. Her legs shook as they struggled to support her weight. "Wha... what happened?" she groaned. Everything ached, and she was glad it did. Pain meant she was still alive to feel it.
The heap of shadows answered her in a deep, masculine voice, laced with pity and scorn. "An ignorant and naive young mare whose reach far extended her grasp learned the importance of proper protections when contacting the lands of the dead."
The voice was new to Twilight, but the roiling darkness was unforgettably familiar. "King Sombra?"
"Indeed." Sombra blinked, and Twilight realized his eyes were nearly indistinguishable from hers, the sclera white and not leaking fell magics. "You are a very fortunate pony, Twilight Sparkle," the shade continued. "Had I not intervened when I did, your body and soul would have been forfeit to malignant forces far beyond your ken."
"Why did you intervene?" asked Twilight. After a moment, she added, "How do you know my name?
Sombra had no lungs, but that apparently didn't keep him from sighing. "You exposed yourself more completely than if you had pressed your nethers against the veil between life and death." Twilight found herself too horribly mortified to respond. He pressed on, either ignoring or not noticing her reaction. "It is obvious that this was not intentional. Had you known of the necessary abjurations, you would've surely employed them against the dark, terrible being you believe me to be. As for why I saved your life? I did it because, contrary your misgivings, you have my deepest gratitude."
Twilight fell back on her haunches. "Whuh?"
A trace of amusement colored Sombra's voice. "Why wouldn't I? You have ensured the safety of my people, returned the Crystal Throne to its rightful heiress, reconciled the Empire with the Equestrian diarchy; in short, you have corrected every mistake I made during my disastrous reign."
"But, but Princess Celestia—"
The umbral mass shook his head, or at least the bit with eyes on. "Celestia is not exactly unbiased when it comes to her foes. She likes to see the world simply and starkly, in absolutes of light and darkness, even as she lives and works in reality's shades of grey."
Twilight leapt back to her hooves, her exhaustion forgotten in her indignity. "That's not true!"
"Oh?" The amusement returned. "Less than a month ago, she sent some of her most capable servants to acquire a newly available political resource before her rival leaders could even react. They even eliminated the only other party with a valid claim to that resources, the better to ensure Equestrian supremacy."
The mare stood silently in confusion, working through Sombra's doublespeak. After a few moments, she scowled. "She sent my friends and me to save a nation from a cruel tyrant and welcome it back to the world."
Sombra's form pulsed in a way suggestive of a shrug. "Semantics. But I did not save you from your own ignorance to debate political philosophy. What do you know of me, Twilight Sparkle?"
She snorted derisively. "What, don't you know?"
"Of course I do," came the calm reply. "I ask because I want you to hear yourself say it. Verbatim, if you can."
Twilight's mood lightened a bit. It was almost like an oral exam; one she was prepared for. "One thousand years ago, King Sombra, a unicorn whose heart was black as night, took over the Crystal Empire. He was ultimately overthrown, turned to shadow and banished to the ice of the arctic north. But not before he was able to put a curse upon the empire. A curse that caused it to vanish into thin air."
"You see?" asked Sombra. "Not a jot of concern for my motives, my goals, my origins. I am merely the villain of the piece, a straw pony that the sun and moon could heroically smite."
Twilight rolled her eyes. "Which is exactly how you behaved – a nearly mindless tide of malevolence intent on enslaving the Crystal Empire and spreading hatred and tyranny throughout the world."
Sombra glared at her. His eyes glowed with a harsh white light, a sharp contrast to his writhing body of gloom. "That abomination was not me. It stole my face, perverted my life's mission. You know nothing of me, Sparkle. Nothing." He paused, sighed, and relaxed, his form going still, his eyes returning to normal. "And I wish to rectify that."
Twilight swallowed. She'd taken a few steps back from the furious shade. She retraced them now. "How can I trust you?"
Sombra's gaze stayed steady, but where there had been rage, now there was sorrow. "You owe me a lifedebt, Twilight Sparkle. I do not know what has become of the old traditions in these past thousand years, but in my time, the savior could make any one request, and the saved would have no choice but to fulfill it. However, I would rather you heard my story of your own free will."
This got a suspicious scowl. "And if I do, what will you ask of me instead?" she asked.
"Nothing. The living should not be beholden to the dead. It is not my place."
"But you'll still use it to make me listen to you," Twilight noted.
"If I must." Sombra's form rippled and flattened, as though making himself comfortable. "Must I?"
Twilight thought about this for a few minutes. Ultimately, she followed the shade's example, lying down. "I'll listen," she allowed. "For posterity's sake if nothing else." Her magic took hold of a transparent crystal pillar the size of her head and carried it to her side. A moment's greater focus, and the gem began to glow from within with magenta energy.
"A recording crystal," observed Sombra, his eyes wide.
"One of the first exported since the Empire's return," Twilight confirmed.
After nearly a minute of silence, Twilight quirked an eyebrow. "Well?"
Sombra shook himself, jiggling a bit. "My apologies. It... Well, it will be clear soon enough." His gaze a thousand years away, he began.