“And, confronted by the one of those responsible, and driven to protect that she held dear, the elder sister committed an act she would never be able to take back…”
Celestia paused mid-speech, her words trailing off into silence. Her etes bored into the last remnants of the flames in Twilight’s hearth, which had died down somewhat over the course of the alicorn’s recounting of the past. The once bright flames were now a dull, smoldering red that cast an ominous shadow across Celestia's features. Twilight watched her, a lump forming in her throat. She glanced into the fire herself, and with a quick flick of her horn, restored it to a full, pleasant burn. The flames swelled and blossomed with a low rumble, and the crimson shifted into a gentle flickering yellow. Celestia blinked, drawn from her silence by the sudden shift in light. She turned to Twilight, her composure well intact. But there was something hiding in her eyes, now. Something grim.
Twilight did her best to swallow that stubborn lump. "What happened?" She asked. "What did you do?"
Celestia opened her mouth to speak, but no words came. She closed her eyes and took in a long, deep breath. When she spoke next, her voice was thin. "...Do you recall what you felt the day you fought Tirek?" She asked at length.
Twilight made an effort not to remember that moment, truth be told. But the feeling had left an irrevocable mark on her mind, heart, and even soul. As such, her answer came with no hesitation, and no dishonesty. "At first? I was scared. I ran away the first chance I had. I just wanted to get away and protect what you, Luna, and Cadance trusted me with. But after he blew up the library? After he almost killed Owlowiscious?"
Twilight felt her hooves curling into the cushion beneath her at the memory. The horrific rush of panic, the frantic haze, and the flurry of activity before it was all turned to heat and fire. There was a tingle in the back of her head that she knew better than to deny. "I was angry. Furious, even. He'd done so much damage. He’d hurt so many ponies. And because of what he'd done, I had to carry so much responsibility. Everypony was depending on me to keep them safe from him. And after he destroyed my home…"
She paused, the last sentence refusing to escape her. But Celestia was not so reluctant.
"You fear that, had you been given the opportunity, you would have killed him."
It was not a question
Twilight lowered her head, a slight burn of shame creeping up her spine. "...Yes," she relented weakly.
Celestia was quiet for a few long seconds, her features tight and her eyes focusing on something only she could see. "We found one of the ponies responsible for what happened to that town. He was hiding in the basement of a large home, driven into madness by his own guilt, and the hatred of the Windigo's winter. He blamed us - Luna and I - for all that had happened. He held us responsible for the lives he had taken, and what the world had turned into.”
Twilight’s eyes flew wide. “What? Why in the world would he come to that conclusion?!” she asked in shock.
Celestia frowned. “As I said. The winter created many things in many ponies. Hatred. Malice. Madness. And in that state… he attacked us."
Twilight flinched, and all at once, she feared that she knew where this was going.
Celestia continued. "At first, I only wanted to run. I wanted to flee and bring my little sister as far away from that graveyard as I could. Every action I had taken up until then was done only in the name of protecting the only family I had left. But when I saw him put his hooves on her. When I heard her screaming in fear and pain…”
Celestia turned her eyes back to Twilight. "I was overcome with anger. Fury. My objective changed. I fought back… and I killed him. It was the first time I had ever taken somepony else's life."
Twilight had to fight the urge to flinch. She had seen her mentor fight before, yes, but there had always been a pristine grace to it. She had fought to defend her subjects out of love. But this…?
“I… I knew you probably had to kill ponies before,” she commented weakly, tracing circles into the floor with her hoof. “Equestria wasn’t always a nice place… But… I don’t know. I didn’t think it happened when you were so young.”
Celestia nodded. "I was forced to grow up far too quickly. And killing a pony like that? It changes you, Twilight. Much like any other forbidden act. There is a terrible liberation that comes with it. When you steal once, lie once, drink alcohol once. It feels as if your chains have been broken, and new possibilities appear to you. When you kill somepony - especially the way I did, it… if you let it, if you are not careful, it can - and it will - make a monster out of you."
"But you didn't let it," Twilight deduced quickly. "You reigned yourself in. The pony sitting in front of me is proof of that.”
Celestia said nothing, and a pit formed in Twilight's chest. She swallowed heavily.
"Right?"
After a prolonged and painful silence, Celestia shook her head. "No… I was a child, Twilight, and the world around me had changed so fast, and into something so impossibly awful. I was barely thirteen years of age, and already I had witnessed more deaths than most ponies ever do in their lifetimes. At every turn, it felt as if the world was out to get me. I was not prepared to carry the weight that was hoisted on my back. And as a result, I allowed my mind to wander roads best left to gather dust…"
Twilight nodded heavily. "I… I think I understand…" she said quietly. “But… you did overcome it, eventually.”
Celestia nodded. “I did… but at great cost.”
The two fell into silence for a few long moments after that, staring distantly into the flames. Over the faint crackling of the embers and the low rumble of the winter wind howling outside her window, a new sound reached their ears.
Children’s laughter.
Twilight turned, her attention pulled to the window, and she recalled the young ones she had seen playing in the streets of Canterlot before Celestia arrived. A tender smile graced her lips, then, and she leaned comfortingly into Celestia’s side. “What happened next?” she asked quietly.
Celestia hummed softly. As if on autopilot, her folded wing unfurled and draped comfortingly over Twilight’s withers, pulling the smaller alicorn closer to her side. Twilight couldn’t help but giggle quietly at the small gesture. She was reminded of when she was younger when her teacher and princess would tell her stories - or read the newest studies at Twilight’s insistence - before a warm flame. A distant memory, but a cherished one all the same. And if the smile on Celestia’s face was any indication, it was much the same for her.
Once more, her voice brought forth the story of her distant past.
“The elder sister fought to defend her sister. And in the end, she killed. The blood that marked her hooves also painted her mind, staining it. She allowed hatred into her heart, inviting upon them the howls of the storm and the hunger of the ice once more. Undeterred, she strode into the midst of the blizzard as if she were a raging wildfire. She became all-consuming… and indiscriminate.”