//------------------------------//
// Royal Musings 
// Story: Fuel the Eternal Flame | A DOOM MLP Crossover 
// by NotAnEditor 
//------------------------------//

Another green fire bursted through the air, magically dispersing a rolled up scroll. It dropped onto a pile of many more similar messages. Purple wax stamps held them closed with the initials TS across it. Obviously standing for Twilight Sparkle.

A heavy sigh broke through the cozy, pinkish-purple colored room. Right next to the pile was a large purple cushion and golden pillow roll. Occupying the bed-like combination was Princess Celestia, laying stressfully as she set aside the letter she was already reading to look at the most recent one.

The princess of the sun seemed very concerned with the letters. Not only the quantity, but the contents of them as well. They informed her of what the ponies of ponyville referred to as apple-lava. Twilight would go on and on about how much everypony loved them except her and her other five friends.

The most worryingly written letter from her protege was on the topic of Apple Cider Season. However, she said that the main attraction would be the apple-lava. Everypony was so excited to try it.

The last portion of the most recent letter Twilight had sent was asking why she hadn’t been writing back, however the issue is that she was! Princess Celestia had written several letters in response, calling her to Canterlot for a meeting and attempting to communicate with her. She recalled repeatedly writing “DO NOT LET ANYPONY DRINK THE APPLE-LAVA” many times throughout them.

When she sent them though, there was not a single acknowledgement of her replies. She had pondered about coming to Ponyville to meet with Twilight directly, however all attempts were halted by the many arrangements she had to organize across Equestria.

She had to get together several special regiments of the royal guard out in these new Hazardous Containment Units. Luna had begun demanding them be sent out with all these reports of monsters and… strange grotesque fleshy masses. The guardsmen had begun referring to them as effigies.

Celestia wasn’t exactly sure what they were about, but from what she heard they were not good. Especially those tall, horrific monsters she was hearing about. Kidnapping and maiming innocent ponies. She was horrified to read about how two Elements of Harmony were attacked by two of the same beasts, so she agreed with Princess Luna, forming and sending them out. 

Princess Celestia sighed. Everything is so crazy! she reflected the letters Twilight had sent her. As she furled up the most recent message, the sound of her bedroom door creaking open alerting the sun alicorn from her reading session.

“Sister.” Princess Luna greeted firmly as she creaked the door open with a hoof.

Celestia loomed her head behind her to greet her sibling. “Good evening, sister.” she waved a hoof, an unhappy look across her face. “What are you doing here?”

“Just checking on you.” Luna replied, coming into the room. The door closed behind her as she entered. “What is all of this?” the moon princess looked down at the pile of letters with a curious look.

“Letters from Twilight.” the alicorn sighed. “A lot of them.”

“What all are they about?” her regal sister queried, picking one up with her dark blue magic and beginning to read.

Celestia looked down at the ground. “Those monsters ponies have been spotting all across Equestria, some liquid she called apple-lava, and a floating cube artifact.”

Princess Luna froze up a little at the mention of apple-lava. “It is just as I feared.” she set a hoof to her chin as she read.

“What was that, Luna?” the sun princess asked.

“Nothing.” she replied, taking a seat next to her laying sister. “A drinkable, red electric liquid?” she guessed what the apple-lava looked like.

Celestia nodded. “Yes. The letters say that it's making ponies act strange."

Luna lowered the scroll and rolled it up. “Have you replied to her?”

“Yes. Although, it looks like they aren’t getting through.” the tall white alicorn responded.

“Perhaps it has something to do with Spike?” she suggested.

Celestia looked away from her sister, at her warm and cozy campfire. “I think so. The letters mentioned him drinking that substance.”

Princess Luna nodded in response with a somber, knowing look.

Her sister looked up at her. “Is everything okay?”

“Do…” she swallowed a little, fear growing from the suggestion. “Do you believe this has to do with our precursors?”

“Precursors?” the suggestion surprised Celestia. She hadn’t recalled them for a long while. "They have been gone for thousands of moons! There is no way they have anything to do with Equestria now.”

“Is that so?” Luna turned, walking towards a nearby window. “Follow, sister. I must show you something” she urged.

Celestia gave a curious look before rising to her hooves and following Luna. She stopped next to her sister, looking down across Canterlot. Multitudes of medieval, castle-like structures spread out in a labyrinth. Even the mountain way leading up was blocked by powerful brick walls. All bright white, purple and gold.

“Don’t you see it? Our architecture, our tapestries, our stained windows. Even the language we are speaking right now.” she explained as her sister looked across their home. It was so long ago since they had waved goodbye to the past rulers of Equestria.

Celestia sighed. “I see your point. However, what would this have to do with all the strange occurrences?”

“I will show you, sister. Come, follow further.” Luna knew much more about Equestria’s past than Celestia. Those memories were much more recent to her, and she was always way more fascinated with them. The recollection of their precursors was very faded to Celestia however. With immortality often comes forgetfulness of occurrences so long ago.

The princess of the night started out of Celestia’s reading room, heading down the stairs of the tower it resided in. Her sister followed closely. Luna had followed this path many times, leading her down into their throne room.

Celestia followed slowly, not understanding where she was being led once they passed their royal throne. She couldn’t help but glance up at the many stylized stained windows, thinking back to what her sister had told her recently.

Luna stopped, turning towards the back portion of the throne. There on the back sat a tall and long tapestry of the two sisters flying together, horns interlocked to share their magic. It was fairly standard.

“And you brought me here for what?” The sun princess looked around for something out of the ordinary.

“Not yet, sister.” Luna casted an aura around the tapestry, leaning it to the side to reveal a small panel on the back of the throne, gray and unlit as if there was supposed to be a light in it. She began charging a bit of energy from her horn, Celestia watching curiously as she shot the magic into the button.

It suddenly lit up, now green from the energy. She lifted her hoof, pressing into the bright button. Celestia’s ears perked, looking around as a small rumbling sounded around them. “Is that supposed to be happening?” she questioned as the ground below them began sinking.

“Yes, it is.” Luna responded.

The polished white floor below them began descending into the ground. As they sank deeper, the slot where the clean floor once stood was slid over with another hidden floor designed to cover the secret elevator once it descended far enough.

Once darkness consumed the elevating platform, Celestia lit her horn to see around. The surrounding walls that slowly exposed themselves was one large mural. What surrounded the two was a giant display of several bipedal beings in knightly armor, spears, swords and other weaponry of the sorts in their hands.

On the other side of the mural showcased a swarm of horrific monsters. Very comparable to what her containment units had so often come across. There were slight differences however. Some were smaller looking, more ape like. Other more brutish looking beasts with a tall, beefy build joined them. It was a very awesome battle between the knights and monsters.

Celestia looked around at them, not really too shocked. She knew what both creatures were up there. The knights, the precursors. Those that were here before them. They came from a different world, Argent D’nur. 

They were strong and intelligent bipedal creatures. They shared a similar form of magic from their homeworld, a special type of energy. Wraith energy. They had left the ponies alone ages ago; however, the civilization disappeared without a trace once they had given them independence. They called themselves the Sentinels.

In the center of the mural between the demons and the Sentinel warriors stood one, standing on a pile of the monsters’ corpses. He was in unique armor, one that covered his face in a helmet with a cage-like design on the front. His left arm was covered in strong leather and metal plating with his torso armor broken open and exposed to reveal his muscly core. 

In his right hand he wielded a long energy blade, curving into two sharp edges at its end powerful old ponish runes extending down the energetic sword. Celestia had remembered him. The second she saw the mural she gave her sister a worried look. The elevator stopped, the hidden room it led down to lighting up automatically.

Torches along the ghastly gray metal and stone walls lit brightly with the trademark color of most wraith energies. Light blue flames grew in wall-mounted torch holders across the large underground library. It was a circular room with one big crystalized table in the center. It was similar to the Cutie Map, several metallic chairs sat around the crystal table. At the side of the table that faced the elevator sat their two seats side-by-side.

As she looked around more and more at the hidden library and its shelves that were carved out of the metallic walls, it became more familiar. This was where they met the former kings and leaders of the Sentinels. Several other chairs were reserved for them as well which, in the foreseeable future, would be left unfilled.

Celestia moved into the room without following her sister, stopping beside their two seats. She could recall sitting here and staring around at the alien race. It was strange. They were honorable and noble yet barbaric and battle-hungry at the same time. Perhaps it was just the different leaders, although the sight of them consuming their meat-based meals would’ve made any young pony ruler gag.

Just across from the table at the arch of the circular room stood a circular formation made by two metallic arches. A slipgate, the main way that most Sentinels traveled. It would make a vortex and transport them to the other set destination.

“What have you brought me down here for, Luna?” The princess questioned, looking around the library and attempting to recall all the hazy memories. “Please do not tell me you are suggesting what I think you are.”

Luna had passed her sister, looking around at the many novels and books on the shelves. “I believe I am, sister.”

“But… We’ve lost connections with the Sentinels centuries ago!” Celestia stated. “Their culture is based around war and fighting! They are completely against what we stand for.” The white alicorn protested. 

The princess of the night nodded, turning to her sister. “Yes, yes I know. But perhaps that is exactly why we need them.”

Celestia thought for a moment, looking back at the mural. Particularly the monsters to the right of the energy sword wielding leader. Demons… 

“I have been cross-referencing texts. Searching for why we have lost them.” She floated a couple of books from the shelves, flipping to pages she had bookmarked before sliding them in front of Celestia’s chair.

The white alicorn went by, taking a seat on her chair, the back of it marked with her cutie mark. She began looking over them, reading about the enemies of the Sentinels.

“I believe they’ve been overtaken by the demons.” Luna said as her sister read on, fear growing in her eyes. “We must take action before the demons overtake us as well, sister.” the text agreed with Luna’s notion, speaking much of wars the Sentinels and demons took part in. According to the book, it was a rather one-sided fight.

“But the ponies, what if they find out?” Celestia asked.

Luna rested a hoof on her sister’s shoulder. “Would you rather let them learn the truth, or suffer under whatever these invaders have planned?”

The taller sister pondered thoughtfully, before sighing and agreeing internally. “...How would we even go about this? Even if we could transport an army, we cannot mobilize an entire legion just because of these small threats.” she pointed out. “You said that their civilization had been defeated by the demons anyways.”

The moon princess looked toward the mural back at the elevator. “Him.” she stared at the lethal looking figure standing on the stone. They both looked towards the depiction of him with a mixture of respect and fear. Celestia had met him long ago. It was the final meeting they had before their contacts with the Sentinels were lost.

Pained, tortured eyes that glared through the gnarled gate that was the front of his helmet. The ever-present, alert and alarmed scowl searched into every portion of her soul, not speaking a word. He had come with the king and commander, third in command of the Sentinel legion at the time, a very recent addition.

It was said once before that he spoke. However all it was were meaningless ramblings of demons as well as the mass slaughter of them. Although by the time they met, the broken and shattered soul refrained from a word of speech.

Luna knew the warrior much better, having read numerous texts on their culture and history. The Great Slayer, the Hellwalker, the Unchained Predator, the Beast and by his enemies: The Doom Slayer. Sentinel legend spoke of how waves of demonic hordes would be slain by his fervor.

“Luna, I don’t think you sho-”

“We must.” Princess Luna interrupted. “They are coming. On the horizon.” she looked back at her sister. “You wouldn’t believe the horrors I have seen in the dreams of our subjects. Unspeakable sights, disturbing torturings, the harvesting of souls.” her voice grew a tad shaky. “Something within those nightmares held me back. I could not interrupt them, I-I’m not even sure I was strong enough to do so.” she made a shaky sigh. “These terrible dreams are not reaping our ponies for no reason, Celestia.” a genuine look formed in her blue eyes.

Celestia closed her eyes, weighing her options. “...Fine. but I have to ask, where are you going to find this Great Slayer?”

Luna looked at a tapestry hanging down one of the walls, a couple of sentinel knights standing guard below their two cutie marks. A gift to symbolize peace between the two worlds. “The moon.” or so, that’s what the myth stated. “Where all mighty beings are contained. If he were anywhere, it’d be there.”

“Ingmore Sanctum.” Celestia muttered the more official name of that realm. Nightmare Moon was not banished literally to the moon. It was a name given to the realm of contained souls. Spheres containing the souls of gods and powerful demons alike. 

“I shall search for him there.” she began. “If I do find him, we will return here. I will try my best to keep him in the hidden library if nothing has commenced once we’ve returned.”

The fellow princess sighed. “Just be careful Luna. We know very little about this 'Great Slayer.’”

“Do not worry, sister. I’ve studied enough to understand his motives.” she turned, clopping towards the slipgate at the other end of the library. “You must handle the moon for the week that I am gone. Transporting there is a long journey from other perspectives.”

Celestia nodded as Luna engulfed the slipgate arches with her magic, igniting the portal open. The vortex that shared the color of her aura swirled, waiting to swallow Luna towards her destination. “I will.” Celestia responded.

“I shall return before you know it.” Luna said, heading towards the portal. The alicorn faded into the vortex, sparks flying as she crossed.

Once her sister was gone, she turned and headed back to the elevator, spotting a similar button that was hidden behind the throne. She pressed it in with a hoof. The elevator slowly rose, returning her to the throne room. 

Once she reached the top, she took a deep breath before starting for her throne. It was going to be a long week without the aid of her sister. However she'd have to keep a close eye on their kingdom. Just as she got comfortable in her throne, she heard loud clopping rushing down the hall on the other side of the throne room’s large doors. They suddenly burst open, revealing a panicked pegasus.

"Princess Celestia!" A dark blue stallion rushed in. He was lanky and skinny, wings across his back. Obvious candidate for the role of an emergency messenger.

"What is it?" she asked her subject as he desperately caught his breath. He had been running for a very long time, weakly making his way towards his princess. Worry grew in the white alicorn at the sight of his panic.

He dug swiftly through his saddlebag, clambering up to the throne. The pegasus took a scroll out, bowing before her before accidentally dropping it from his maw.

It rolled up towards the throne, Celestia lighting the scroll in her aura and lifting it to her gaze.

"P-P-Ponyville! Under attack… huge monsters!" he briefed, totally out of breath.

The princess continued reading, eyes expanding as more of the truth exposed itself. This can't be true. She thought. They are coming…