Even though the Omega Timeline was simply a white void, after Nightmare conquered it the place somehow became darker.
Instead of colorful shops and houses, now most of the buildings were destroyed.
Instead of happy chatter, now the only sounds were harsh conversations.
Instead of people mingling and hanging out, now the only inhabitants were Nightmare's cohorts, who mostly glared at each other and sometimes fought.

The main square, the heart of the Omega Timeline, was now the location of the center of the operations, Nightmare's "palace": in reality, it was just a big dark tent with a throne placed inside, but the Guardian had standards, and demanded to be treated as the ruler he was.

Currently, said ruler was checking the Multiverse through a code window, deeply displeased.

His plan had been a real genius one: following a hunch, he confirmed with Fell!Science!Sans that the Omega Timeline wasn't just a meeting point for AUs, but more of a multiversal interface. It could be used as a meeting point because code manipulation was way easier and accessible in there, even though it seemed no one had realized it; an expert in coding could have used this to their advantage and reshaped the Multiverse to their will, but Nightmare was not that good, so his plan had been much simpler: infiltrate the place, and then erase as much positive AUs without killing their denizens once he was inside.

The rush of negative emotions generated from his actions had been delicious and empowering: thousands and thousands of people had lost their homes in an instant and they didn't know why, leaving them full of fear, uncertainty, grief and hopelessness, and they would soon begin to feel angry, resentful and desperate. On top of that, the boost these feelings granted him had allowed him to destroy and conquer the only place where they could have found help, dooming them forever.
Truly a masterpiece.

And yet.

And yet, Nightmare had checked the code window a couple of days after his victory, trying to see if there was anything else he could do, and it was displaying something that made no sense, something that he tried to correct but kept appearing again and again.
This was all CORE's doing, no doubt.

The Guardian clenched his fists and his appendages curled, and started to once again work on the code, when he felt a well known presence in the air and smirked, closing the code window with a wave of his hand. One of his men called him from outside with a shout.

"Boss!" Underfell Sans entered, followed by the Snowdin Canine Unite of his AU. Even if he wasn't his brother, the Royal Guards still respected him and feared him, Nightmare could feel it.

"We found him home, tryin' to sneak around." he then moved to the side, to show a beat up Dream in the arms of Dogamy and Dogaressa. His clothes were tattered, his bones were scratched and his arms were tied behind his back. Smug satisfaction rolled off of the king in waves.

The positive Guardian looked up at his twin and glared. Nightmare could feel fury and, surprisingly enough, hate, coming from him, though they were faint compared to the ever present guilt Dream felt in his presence and the sickeningly positive aura of the Golden Apple.

Nightmare got up from his throne to slowly walk in front of his prisoner, enjoying every second of it. Dream rolled his eyes, feeling a twinge of exasperation at his brother's antics.
The negative Guardian frowned for a moment; his twin always thought he was better than him.

He soon regained his smirk when one of his appendages moved closer to Dream and lightly enveloped his neck, making the yellow clad Guardian feel one of Nightmare's favourite emotion: fear. The guards let him go and moved back, unwilling to be near Nightmare longer than strictly necessary.

"Hello brother" he purred "it's been a long time since we've last seen each other, hasn't it?"
"If only it had been longe-agh!" the appendage tightened its grip.
"Now now, that's no way to talk to your big brother. I was simply concerned for you, Dream." His twin sent him a deadpan look, and Nightmare was reluctantly impressed with him for defying him so openly.
"After all, you went into hiding after I conquered this place. All of my men were looking for you. Aren't you lucky to have such a caring twin? Who knows where you were, what you were doing, who you were with..." he emphasized his words with another squeeze of his brother's neck.

Nightmare felt scorn coming from Dream, who answered with a chocked voice: "You're delusional if you think I'll tell you anything!"

The tar covered skeleton mockingly shook his skull. "You are always so stubborn. " He then turned toward Underfell Sans and the Canine Unit. "Leave us."

After the other monsters left his palace, Nightmare focused back on his brother.
"Dream, I'm giving you one last chance. I know you were with CORE-"
"Frisk."
"-trying to undo all of my work. You either tell me what you were doing, or I'm going to make that little brat come to me and tell me themselves."
Dream's only response was a glare. Nightmare huffed.
"The hard way it is. Can't say I mind, though." He sneered, then walked even closer, till his face was only inches away from Dream's "I know you're watching child: I want to have a chat with you, so come." Both twins looked around. Nothing happened.

"Let's see for how long you're willing to make your friends pay for your mistakes."
He grabbed the other's ribs.
"We're due for some brotherly bonding anyway." He suddenly snapped the rib he was holding in half.

Dream pained screams filled the air.

===============

Dream couldn't take it anymore.

Nightmare had been torturing him for hours, and the glee his twin was feeling at his misery was only making the situation worse, giving both of them extra energy and creating a vicious cycle: Dream couldn't faint and get a reprieve, while Nightmare was only becoming more creative. The fact that they were soulmates and the bond prevented him from killing him was little comfort for the positive Guardian: after all, that didn't stop him from trapping him in a stone statue for half a millennium.

It didn't matter: Dream was a Guardian, and he could take it, he had to, for everyone who was counting on him.

But it hurt.
It hurt a lot.
Even more than it should, because Frisk wasn't coming.

And Dream knew that they shouldn't, that they couldn't teleport him away or fight Nightmare, he knew one of them should keep helping the thousands of refugees that were still lost in-between AUs, he knew this was just a trap, he knew, he knew, he knew...

But he wanted Frisk to come anyway. He still felt abandoned and betrayed.
Obviously Nightmare noticed, and stopped what he was doing.

"Poor Dream" he drawled "all alone at the mercy of his enemies, who only want to hurt him. With no one to turn to. Betrayed by the one he trusted the most."

The unsubtle reference to their shared past filled Dream with guilt, and once again he wondered whether his brother was too far gone: the bond told him that he was still there, that his torturer was the same Nighty who used to read him bedtime stories, but nothing more.
He didn't know what would be worse: the corruption still poisoning Nightmare's mind after so long, or all of his actions being completely his.

Dream just looked down, defeated, with tears in his eyes.

Nightmare patted his skull in a parody of comfort. "I know I know" his tone was saccharine. "I also want them here. Come on CORE, do it for Dream."
"My name is Frisk."

The positive Guardian widened his eyes, seeing the child behind his twin. "Frisk don't!" his throat was once again constricted by his brother's appendage.

"Finally. You know kid, it's rude to keep a king waiting."
"When I meet a king, I'll follow your advice."

Dream let out a short laugh and let his petty amusement shine through to annoy Nightmare; it worked, but he didn't let it show, choosing to ignore his childish twin.
"I'll go straight to the point." he conjured a code window, far enough away that CORE could see its content, but not touch it. "I want you to stop." he grinned at the child, who glanced at him and then started reading. "Being locked in a struggle of creation and destruction won't do us any good. If you don't stop, be sure I'll send my army after you and all your little refugees. Do it, and I might be swayed toward mercy".

CORE finished reading and said in a neutral tone: "I don't know what you're talking about". The brat thought they could fool him with their innocent act, but the smug satisfaction coming from them said otherwise. Nightmare snarled: "Don't play dumb! Stop recreating the AUs I destroyed! I know it's you!" the negative Guardian let out a deep breath and regained his composure, but before he could speak again he was stunned by the sheer shock and hope coming from Dream.

Nightmare couldn't stop his own confusion from showing: why would CORE hide what he was doing from his brother? It didn't make sense... unless the brat wasn't sure, because they weren't responsible.

Focusing on the child's emotions, Nightmare noticed that CORE was also relieved, so he knew he had had the right idea. "Who's recreating the AUs?"
CORE mirrored his earlier smirk and answered: "You really don't get it, Nightmare? I thought it was pretty obvious. Who could possibly recreate AUs, beside the Creator themselves?".