“Princess…”
The darkness swallowed Reaper’s voice.
“Priiiiiiincesss!”
Reaper’s horn glowed, casting deep shadows throughout the ruined hall.
“Oh, let’s not do this, please!” he called out, walking toward the back of the chamber, picking his way over broken stones and roots.
“You know I don’t really have any particular power in the dreamscape, so finding you is going to take time we honestly don’t have.”
He ducked under a crumbling arch and noticed a darker shape huddled in the adjoining chamber.
He sighed and moved closer. “There you are, Princess...and what’s that you have there?” he asked, noticing her poking at the shattered remnants of a tarnished helmet.
“Hmm,” he mused, “what’cha doing?” He sat down next to Luna and looked at the various fragments of Nightmare Moon’s ruined armor and harness. She appeared to be piecing it back together loosely, like a broken puzzle.
“Ah. So I take it your “reconnaissance” didn’t go well?” he asked.
Luna turned her head toward Reaper and stared into his eyes. Tears welled in her own eyes, and Reaper’s horn-glow glittered in the black pools of her dilated pupils.
“I have seen more than I ever wanted to, Harbinger. I went back to the very foundations of my shame and pain, and looked for the darkness to manifest. I watched the first nightmares I ever inflicted on the ponies of this world.”
Luna closed her eyes and let her head droop.
Reaper waited silently, listening to the scrape and clank of the harness bits Luna was pushing around.
Luna took a deep breath: “I believe I found the original occurrence of the darkness,” she said. “Do you recall the passing of a pony named Sea Foam?”
Reaper raised an eyebrow. “How long do you think we have, Princess?” he asked. “I can recall at least 75 ponies by that name over the last 1000 years without even trying.”
Luna nodded: “I understand, but this Sea Foam would have lived almost 900 years ago.”
Reaper chewed his lip and pondered for a minute, his eyes focused off in the distance.
“An earth pony stallion, pale green?” he offered.
“No. Just after him--an old cream-colored mare.”
Reaper shifted his gaze up to the darkness above, and blinked slowly. “Nooo…” he said tentatively.
“I’m not surprised,” Luna responded, “she was a hermit, living in a thinly-populated region. I find it unlikely you would find a trace of her in anypony’s dying memories.” She rocked forward and laid her chin on her crossed hooves, staring at the half-reconstructed fragment of her old breastplate.
Reaper agreed: “Yeah, a hermit would certainly leave little or no trace in any other lives. And you’re sure this is a true vision?”
Luna levitated and manipulated the breastplate pieces, welding them back together, tipping her head sideways, examining the result.
Reaper furrowed his brow. “Collecting souvenirs, Princess?” he asked quietly.
She blinked slowly, attaching a length of chain with a pale flash.
“I find it helps me reconstruct my memories, if I reconstruct some of these old mementos.”
She stood suddenly, and let the half-finished cuirass fall to the floor with a clang.
She turned to Reaper as he climbed to his feet: “You asked if this was a true vision. Let me show you…”
They stepped out of the banner-portal onto a windswept, frozen heath. An old pale mare ran by, breathing hard, stones flying up from the ground as she thundered by at top speed, with Nightmare Moon in close pursuit.
“What do you want?!” cried Sea Foam, swerving around clumps of grass and low shrubs in a vain attempt to evade her pursuer. “Why do you haunt my dreams?!”
“Because of what you did, you bitch of a sister!” Nightmare Moon shrieked, leveling magic blasts at Sea Foam’s retreating form.
“I’m losing them!” Reaper yelled, as he started after the two figures.
Luna placed a hoof on Reaper’s shoulder, and he froze in place as the whole scene seemed to shift perspective and glide directly in front of them, as though on a treadmill.
“Oh--that works, too!” he remarked. Luna stared ahead silently.
“I don’t understand!” yelled Sea Foam. “I’m not your sister! I don’t even know you or your sister!”
“It matters little whether you know it or not, but you are my sister!” cried Nightmare Moon, finally landing a magic bolt on her target.
Sea Foam spilled to the earth, and howled in pain, as her cutie mark--a blue-green spiral--burned away, replaced by Celestia’s sunburst. Tattered, broken wings forced their way up through her shoulders with a ripping sound. A jagged, blood-streaked horn poked through her forehead.
Nightmare Moon dropped from the sky and straddled Sea Foam as the struggling pony rolled to her back and tried to kick free.
Magic bolts struck again and again, leaving welts, gashes and flaming streaks, as Sea Foam writhed and gasped in agony.
“No, please!” Sea Foam pleaded, as Nightmare Moon lifted off the ground and backed away a pace, preparing to rear up, and drive her metal-clad hooves into Sea Foam’s neck.
Sea Foam took the opportunity of that brief break to scurry sideways, and bolt to her feet, knocking her tormentor off-balance. She dashed madly toward a cave opening that had appeared in a nearby rock formation, and dived through the entrance.
Nightmare Moon regained her footing and scrambled after her quarry: “No! No escape! I will have justice for the wrong you have done!”
She leaned forward into the inky opening, horn shining bright with deadly power: “You cannot hide in the darkness, dear sister--I own the dark!"
The air throbbed with energy as Nightmare Moon’s horn erupted with a violet-black burst that swamped the cave, bathing Sea Foam in indescribable pain and horror, which coalesced into a black miasma, spilling out of the entrance, smothering the rock formation, crushing it as though the sea itself had lurched onto the land.
Sea Foam’s unearthly cries of anguish were cut short by the crash and crack of rock, and Nightmare Moon’s howls of tortured laughter.
The whole scene was wreathed in impenetrable darkness for a moment, and as it passed, the scene dissolved away, leaving only a pale moon hanging in the sky, and Sea Foam’s broken body, face frozen in a rictus of terror, which dissolved away into the turf.
Reaper blinked, and found himself again, in the castle ruins, Luna some way away, looking out through a broken window, at a pale moon rising.
"I begged you not to leave me alone with my memories," Luna whispered.
Reaper shook his head slowly: “Wow.”