Ting! Tang!

Celestia froze, turning as bells tinkled softly in the cavernous room. A gray unicorn stepped from concealing shadows, starry hat pulled low over his eyes.

“Starswirl! How—"

“This is a bad idea," he said grimly.

"It's all I can do!" Desperation strangled her voice.

"It is not." They matched stares, eyes hard. "She wouldn't thank you for this. You refuse to cut the root. Simplify. End it, Celestia."

"Do you know what you're asking?"

"Completely. You're strong enough. She could never match you, and the parasite hasn't changed that. How will she curse you, if others suffer in her place?"

"No, I…" Celestia turned, stained glass spilling chromatic wash across her coat. The gems before her sang softly from their pedestals.

"If you had pushed aside equivocation to act, your ponies would be safe. If you were decisive with Sombra—"

"If we had treated Sombra on his terms, we would be no better than him! This will not change that!" Her eyes flashed. "And you! You are out of place, where you should never be! How many jumps will you make, Chronomancer? Intruding, meddling, to sate your curiosity?"

"I'm unsure." Starswirl hesitated. "I'm not done yet. But this isn't about me."

"I will not kill my sister!" Celestia turned back to the Elements. "With these—"

"You can merely delay the problem. The timeline will decay, returning the crisis. They will not handle the parasite. Not for you."

"No." She grit her teeth. "No, there's more. My sister is still in there, still fighting."

His eyes narrowed, flashing. "Truly?"

In response Celestia seized his hoof, dragging him to the pedestals and shoving him at the blue gem. After a moment, he touched it. High, frantic whispers filled the room.

No, no, wait, help, please stop!

He yanked his hoof back, eyes wide.

"Truly. Help me. This can end with better than blood."

Starswirl sighed, rubbing his forehead.

"As you will, my Princess. Prepare; I will lure the Nightmare." Celestia nodded, swiftly gathering the gems. Starswirl began a spell, magic spinning from his horn in wisps and whorls. It moments, it was answered with stars.

"So, sister, I find you…" The vapor coalesced, firming into a mockery of Luna's beauty and elegance. "Hiding behind others still!" The Nightmare's cyan power slashed, barely deflected by Starswirl's skill. Celestia struggled, frantically fighting to bring all six Elements under control. The violence surged, thrust and counterthrust. She supported the magician as she could, but didn't dare divert attention from the trump she desperately needed.

"Starswirl!" Finally, her preparations were complete. All six gems sang under her sway, scintillating with repressed radiance. Nightmare Moon's eyes widened, worry showing as Celestia accomplished the impossible. There was a burst of chroma, crazed colors crackling in rainbow power, and the fight finished.

A fading scream and a scrap of fluttering cloth were left. Starswirl's eyes tracked the fragment, even as he fought to control his panting.

"No wonder you were so surprised to see me." He limped forwards, hooves crunching on shattered glass. Out the empty windows the moon vaulted skywards. A burst of light touched it, imprinting a dark visage, locked in morose contemplation of the planet. "You have delayed disaster by a millennia, when she marked with stars may aid Luna's escape from darkness. Or disaster will fall again, leaving you powerless to resist. Prepare desperately, Celestia."

"Wisdom from your research?" Celestia shakily released the stones.

"Time is a strange mistress." Starswirl raised the dropped rag. It shone with stars, gold needlework brilliant. A single bell tinkled. He doffed his cap, matching the ripped cloth to a seam. "It's said to heal all, but I see a surgeon's scalpel. It cures with cuts, separating us from who we were no less than death." There was blood on the fragment. "Yet perhaps your sister will use it well."

"You can try—"

"Nothing seen can be unseen, nothing done undone. Such is the essence of time." He smiled grimly. "When we meet, Celestia, ages and ages hence, please do not pity me. I love my work, though it has served me poorly. Now even the sanctity of my death is denied." He jammed his hat back on rakishly, and looked to the sky. "But if Luna is redeemed… I deem it worthy." He saluted Celestia. "Be well, my Princess."

There was a pop, a puff of air, and she was alone.