The Devil You Know

Princess Luna, had she been lesser trained, would have stormed over to Twilight Sparkle right then and there, shaking her until the words tumbled forth from her mouth. What had she found? Who was it? Instead, she waited for the lavender unicorn to catch enough of her breath to resume speaking. There was a virtue in patience, even if at this moment she found herself surprisingly impatient at waiting to hear what Twilight had found whilst researching within the library.

Just when the azure mare thought she was going to have to actually shake her companion, Twilight blurted out, "It's a pony that only you know the name of!"

Luna was thunderstruck. "The book said the creature lives within Princess Celestia, and the only pony in Equestria who knows the name is you!" Twilight continued, her eyes wide as she stared up at the Lunar Princess. Princess Luna's reaction was to slowly sit herself down, looking like she might faint.

"Oh no, nooo no no no no no no," Princess Luna said softly, the words coming out in a moan. "Not this. Anything but this."

"Princess?" Twilight asked, creeping closer.

"It's... Daybreaker," Luna explained, the word all but whispered in fear. "The only pony I have ever truly feared above all others, who may very well bring about an end to this world."

"Who is Daybreaker?" Twilight pressed, her words pleading for the story behind the name, both in a quest for knowledge and in supplication to the troops so that they would know best how to fight.

Luna sighed, realizing she would have to be quick about it. "Daybreaker is the darker half of Celestia, as Nightmare Moon is the darker half of me. She is a formidable creature, and a foe beyond our reckoning."

Twilight Sparkle ruminated over this for a few minutes. "Okay, so how do we stop her?" She asked, which only earned her a look of sorrow in return.

"We don't."

"What do you mean?" Twilight demanded, nearly shoving herself into Princess Luna's face. "There has to be a way!"

Luna shook her head slowly. "I have never heard of a way to defeat her, but then again none of us have ever had to actually battle this creature," she said slowly. "So, to my knowledge Twilight, there is no way to stop Daybreaker from destroying Canterlot and Equestria itself."

Twilight frowned at this, then sat down on her rump. "What about... Nightmare Moon?" She asked after a few moments, hope written all over her face. She was grasping at straws, surely, but some kind of plan was better than none at all.

"I beg your pardon?" Luna replied, ears swiveling back and forth in confusion while her nostrils flared in a deep breath.

"Nightmare Moon. She's incredibly strong too, and it took the Elements of Harmony to defeat her with the rainbow friendship laser and bring you back to us, Princess," Twilight said, standing again. "You could bring her forth again, let her fight Daybreaker and bring her to heel."

Princess Luna opened her mouth to object, but closed it again as she thought it over. "How do you intend to defeat Nightmare Moon?" She prompted, hoping that this wild, hare-brained idea of Twilight Sparkle's had been actually thought through and not just blurted forth as inspiration had struck her.

The question only deterred Twilight for a moment, her violet eyes narrowing thoughtfully as she considered. "What do you mean?" She countered, though it was clear the gears were turning within her mind.

"If Daybreaker can be defeated by Nightmare Moon, then how do you intend to bring my darker self down again?" Luna pressed, her own eyes stern with the inquiry. "The Elements of Harmony again? What if the others didn't survive?"

Twilight Sparkle sucked in a breath, but she wasn't about to back down from the closest idea of a plan they had that didn't involve sending any more soldiers to their death from the fiery pony who'd so far been wiping the floor with them. "I'll find a way," she said firmly, while a thought tickled the back of her mind.

Princess Luna stared at her wordlessly for several moments, the silence seeming to stretch into infinities before finally she merely nodded. "Very well," she said softly. "I warn you, she is much angrier than before, and likely won't listen to any commands you try to give her."

Twilight simply nodded in return, remaining on her hooves.

With a sigh, Princess Luna went over to the troops that were lingering near the map, studying it carefully in the hopes that by burning the routes into her mind, her other self would remember them. It was not going to be easy to give in to the darkness, especially when it didn't want to give up and return to the light. Either way, it seemed like this was their best shot. Luna didn't want to think about what would happen should she fail to bring her sister down, so she shoved those thoughts away. They would do whatever it took to stop Daybreaker, even if it meant she had to regress.

A simple nod to the soldiers, who hurried out of the room. Shaking out her mane, she sensed Twilight moving behind her. "My dear, you don't want to get too close to this," she warned, and heard the young unicorn step away again. Princess Luna then closed her eyes, looking within herself to where the darkness lingered in her soul. She knew that her own monster had been locked away after the initial defeat, so once she found the cage she simply undid the locks, waiting for her other self to step outside and take control.

Princess Luna took a shaky breath, then the air chilled around her as the Nightmare came forward to occupy the body and mind. Her azure body deepened to black, her mane and tail becoming a brilliant, sparkly blue full of stars, and armor covered her head, chest, and legs. The change was as rapid as it was thorough, and the slow inhale followed by a little chuckle filled the quiet hall.

"Ahh... So good to be out in the world again," purred the distinctive voice of Nightmare Moon. "Time to go and see what my competition has gotten up to in the town square." She gave no indication of being aware of Twilight Sparkle's presence, and the little mare wasn't about to press her luck.

Waiting, perfectly still, she hoped that her old nemesis was willing to go and seek out Daybreaker instead of hanging around the castle and perhaps raze it to the ground. So far, so good. Mentally crossing her hooves, Twilight Sparkle remained a living statue so that Nightmare Moon would remain focused on the hastily arranged plan. It appeared to be working, so everything was coming up roses.

Nightmare Moon chuckled again, moving towards the doors leading outside. Her hooves rang out confidently against the floor tile, her gait the predatory glide of a panther on the hunt. The air seemed to shimmer around her, magic gathering for the battle that was surely to come. She was hungry for blood, and it seemed like this Daybreaker was as well. A most interesting turn of events since her banishment. Perhaps she would taste Daybreaker's life force at the end of it.

And then, then she would of course turn her sights onto once again destroying the Elements of Harmony and ruling Equestria in an eternal night.