Slayer

By the time Twilight and Celestia had given the all-clear to the survivors of the lab to head topside, the demons had all but vanished entirely. When they headed back into the castle proper, they were just in time to see the guards starting the cleanup process, clearing away rubble, trying to scrape burn marks off the walls, or piling up piles of demon viscera and corpses into carts, presumably to study in the lab once things calmed down.

Princess Luna was in the middle of this, wearing her own personal armor as she directed members of her night guard around. Her stoic facade broke upon seeing Celestia and Twilight, and she gave out a relieved smile before dismissing her guards and heading over.

"I am pleased to see you two are alright," she said, instantly moving in for a quick nuzzle with her sister. If Celestia noticed the small patch of demon blood that rubbed onto her from the action, she didn't react to it.

"I am glad you're safe, as well," Celestia said, before her face grew grim. "Casualties...?"

Luna let out a sad sigh. "We lost a number of guards during the battle, we haven't taken full role yet so we don't know who. Thankfully, we have confirmed that no civilians have perished." She looked past them to the elevator, which was already being loaded with a cart full of demon parts. "And the labs?"

"It was... far worse," Celestia said, bluntly. "We lost a large amount of ponies, both civilian and guard."

The two shared a sad look, but Celestia pressed on. "However, as tragic as it is, we have more... urgent matters."

Luna's posture shifted noticeably, her eyes going back and forth between Twilight, Celestia, and the nearby Aegis, who was busy consoling the surviving scientists. "Is it related to what happened here today?"

Deciding to be direct, Twilight spoke up. "The Slayer is free."

"What?!"

Luna's outburst caused nearby guards to pause in their actions, before hastily resuming at Luna's commanding glare. "What do you mean, he's free?"

Celestia just looked to Twilight, who shuffled uncomfortably. "When the invasion started, I... panicked, and decided to release The Slayer."

"...I see. And where is he now?"

"While he was fighting the demons, the ancient teleporter activated," Celestia explained. "He's now somewhere just outside of Manehattan."

"Then we must go," Luna said, already starting to walk away. "We know not if he can be trusted."

"Ah, I wouldn't worry about that, Princess."

All of them looked upwards at the new voice, revealing Discord casually hovering in the air above them.

"Enough of your games, Discord," Celestia spat, "do you know something we don't about the situation?"

Discord floated down to their level, uncharacteristically serious, all things considered. "Very well. To make a long story short, I took a small trip to Tartarus to do some research of my own."

"And what did you find?" Luna asked, not bothering to give the others time to react.

Discord grinned, but it was a ghost of the smile he usually wore. "The demons are invading because The Doom Slayer was freed."

Twilight felt as if the words pierced right through her. Was this... her fault?

"'Doom' Slayer?" Celestia asked.

"It's what the demons refer to him as. And assuming they told me the truth, he's been their number one enemy for countless eons, even longer than I've been around." Seeing the state Twilight was going into, Discord hastily added, "He was the only one keeping them from invading other realms."

This did calm her nerves slightly, but only enough to not let the guilt consume her. She at least knew that agonizing over her decision could wait until the situation was fully under control. "And what about the demons," she suddenly asked. "Where have they gone?"

"They're probably focusing mostly on combating The Slayer," Discord said. "But I don't know how much they'll try to terrorize Equestria in the meantime. To that end, I went ahead and had the whole town evacuated into your castle. Starlight said something about 'Emergency Plan Delta', so I figured you'd know about that."

Twilight sighed in relief. At least her friends and neighbors in Ponyville would be safe.

"What of other cities?" Celestia asked.

"That's where you and I will come in, Tia. As ironic as it sounds, I'll do what I can to help you keep order in cities, and keep the demons at bay."

"And what of Manehattan?" Luna asked. "Who will go after The Slayer?"

"I'll go," Twilight cut in, interrupting all of them. "I... I let him out in the first place. Hopefully, if he'll listen to any of us, it'll be me."

Luna nodded. "Then I shall go with you. If what Discord says is true, and the demons will focus on him, then it would help to have a capable fighter by your side."

Celestia ignored her sister's thinly veiled bragging as she started walking off. "In any case, we should all prepare, then. This is not a problem that can be solved with the magic of friendship, so we must be ready for the worst."

After a trip to the mostly-undamaged armory, where Celestia put on her own personal armor and Twilight made due with a spare set of normal guard armor, they parted ways, Celestia and Discord heading west of Ponyville to start, with Twilight and Luna making a direct line for Manehattan.

The flight took about ten minutes, during which Twilight brought Luna up to speed about what exactly The Slayer did, and where his loyalties seemed to lie. Luna had simply nodded in response, but said nothing.

By the time they could see Manehattan over the horizon, it was obvious that something was very, very wrong.

Smoke was rising from the city center, and even from their elevation, they could see a massive crowd of ponies fleeing from the city entirely.

Fearing the worst, the two of them made their way down as quickly as they could, landing in front of a local police officer who seemed to be in charge of the evacuation. He was surprised by the sudden appearance of Luna and Twilight, but he quickly recovered.

"Oh, thank goodness you're here!" he said. "It's been mayhem in the city, and- and I don't know what the hay's going on!"

"Were you under attack?" Luna asked, her voice gentle, yet firm.

"Yeah, but it was by nothing I ever seen. They were like the stuff of nightmares! I'm making sure everypony gets out, but no way am I going back in there!"

Luna nodded in understanding. "Keep up the evacuation, then. We'll go in and see for ourselves."

The officer nodded as he resumed directing the stream of citizens, while Luna quickly took back to the air, Twilight following right behind her.

The further into the city they got, the worse the situation appeared. The outer areas only had a few scattered fires and concerning blood stains, but the entire downtown area was completely unrecognizable.

Apart from the myriad fires that were spread among the buildings, it looked as if the roads had been literally paved with flesh, often looking as if it had grown straight onto the walls of nearby buildings, as well.

Speaking of buildings, the ones that weren't collapsed completely had been entirely taken over by this otherworldly, grotesque display, as buildings were often held together by little more than pillars of flesh, twisting in shapes that should not have been structurally possible.

To say nothing of the stench, which was almost enough to make the both of them vomit from the air as soon as it hit them.

"What in the...?" Twilight gasped, unable to finish her sentence. Is this what awaited Equestria if the demons were able to roam free?

Below them, they could see a number of figures moving across the destroyed cityscape with ease, which Twilight recognized as more demons. At some point, they had been spotted, and sent a few fireballs their way to try and shoot them down, but it was easy to simply weave around them, given the distance.

"Where could The Slayer be?" Luna asked, both to herself and to Twilight. "Surely he would not abandon the city entirely?"

As if in answer, at that moment they spotted a particular set of ruins get blown to bits, as another figure ran out from it, the demons quickly converging on it.

Twilight knew who it was before she even got a good look, and she dived down to perch on a particularly tall piece of rubble, Luna following her.

Sure enough, knee-deep in the carnage was the one they had been looking for.

The Slayer, or as Discord claimed the demons knew him, The Doom Slayer.

By now, Twilight had grown numb to his methods, but this was Luna's first time seeing it, and she found herself equally in awe and repulsed by his skills.

"So... what's the plan?" Twilight awkwardly asked, not bothering to whisper due to the cacophony of battle below them.

"Hm? Right, uh..." Luna looked at The Slayer and the horde of demons converging on him, which seemed to be enough to make up her mind. "I shall go down and assist him."

"What?! But-"

"Hush, Twilight," Luna said, pulling out her sword with her magic. "Though it has been quite some time since I fought in a battle of this scale, I assure you my skills have not dulled with age."

Before another word could be said, Luna spread her wings and flew directly into the battle, immediately using her momentum to smash a demon underhoof.

Twilight just watched, terrified as Luna began fighting the demon horde from the opposite side of The Slayer. If he noticed the additional help, he didn't appear to acknowledge it.

For her part, Luna was nowhere near as effective in combat as The Slayer, but she was still more than able to keep up with the demons now targeting her. She fought with a sort of grace, easily able to combine sword use, hoof strikes, and blasts of magic into her fighting style. She wasn't killing demons as fast as The Slayer, but she was still keeping them at bay all the same.

After some time, the demons seemed conflicted on whether they should attack The Slayer or Luna, and seemed to choose whoever happened to be closer at the time. Twilight didn't spot any sort of coordination on their part, but judging by the way they fought, they seemed to operate purely on overwhelming numbers and strength, rather than tactical genius.

Eventually, it seemed that the immediate area was running out of demons, as the horde grew thinner and thinner. Much to Twilight's growing dread, it wasn't long before the group thinned out enough that The Slayer and Luna were now in direct line of sight with each other as they fought. Thankfully, The Slayer seemed to acknowledge her as an ally, and very clearly took care to not shoot at her.

The one exception was when a demon managed to slip behind Luna without her notice, and lunged right for her, only for The Slayer to dive in to intercept the demon's flight path, quickly redirecting its skull into the ground to add to the growing pile of corpses. Luna noticed the assistance, but quickly moved on to fighting other threats.

It wasn't long before all but one demon had been slain, which Luna finished off as she knocked it to the ground and drove her sword into it. Seeing that the battle was over, The Slayer began walking up behind Luna. Once again panicking, due to what happened to Celestia, Twilight chose that time to fly down to join them. "Wait!"

Luna looked over at her interruption, curiously, while The Slayer only gave her a glance as he kept walking. "What's wrong, Twilight?"

As soon as she said that, Luna caught sight of The Slayer walking towards her, until he stopped right in front of her. Though shocked by his proximity, Luna still gave a respectful nod. "I have been told about your fight against the demons. With that in mind, I would like to-"

Just as Twilight feared, Luna's apology was cut off as The Slayer hit her with a punch right in the snout. However, unlike Celestia, it wasn't enough to completely knock her down, and it was easy to see the rage filling her face as she got back up, her own blood streaming from her nose to join that of the demons on the ground. Twilight could only watch, horrified, as Luna reflexively swung her sword at The Slayer in response.

He easily caught the blade mid-swing, and proceeded to effortlessly yank the sword straight out of her magical grip, causing both Twilight and Luna to balk. He then threw the sword, blade first, at the ground in front of Luna, embedding it in the fleshy surface of the street. Without giving her a second look, The Slayer simply started walking away, heading deeper into the city.

Luna stood there, stunned, before she came to her senses and quickly pulled her sword from the ground. This time, though, Twilight was quick to get in front of her before she could chase The Slayer down. "Luna, stop!"

"Thou witnessed it, the cur attacked me!" Luna spat. "I will not stand for such disrespect!"

"Luna, please, he did the same to Celestia, too!"

That was enough to make her regain control of herself. "What?"

Twilight chuckled nervously. "I guess that's his way of paying you two back after you... imprisoned him."

Luna stood there for a moment, before slowly sheathing her sword, followed by reshaping her snout, much in the same way Celestia did. "Very well, then. Apologies for letting my anger get the better of me."

Now that the battle was behind them, Twilight took the time to inspect the ruined city around them. "Just... what are they trying to do?"

"It's part of their plan, I assume," Luna explained. "Back when they invaded after Discord's defeat, they had done something similar to some of the larger villages before we expelled them with the Elements. Still, they had never done so to this scale before..."

The answer presented itself in the back of Twilight's mind, but she did her best to not think about it, and simply tried to ignore the sound of flesh squishing underhoof as she walked.

Up ahead, in the direction The Slayer left, they could already hear the sounds of more combat.

"At least he wastes no time," Luna commented, starting to walk ahead in the same direction. "Whatever his mission here is, I feel it would not hurt to assist him, for the time being."

Twilight nodded in agreement, and they both sped up to rejoin The Slayer.