"Ugh..." Sans groaned.

He sat up in a daze, his skull pounding in pain. It took him a few tries to fully open his eye sockets fully, due to the bright light of the room he was sitting inside of.

It was a rectangle shape, with a door on the other side of the room from Sans. It was closed, most likely locked, too. On the walls next to it was covered in different pieces of paper, all of them crowding the whole wall. He couldn't tell of what they were from where he was.

Sans was sitting on a mattress in the corner, it Papyrus' old one before he bought the race car one. There was a chain extending from the wall, which was connected to a small, metal collar around his neck with a key hole on it. Around his wrist was a glowing bracelet, which he easily identified as a magic blocker.

So, a short cut was out of the option.

Sans couldn't believe what had happened. His brother, Papyrus, was a yandere. He killed those monsters? His so called innocent brother was an obsessed killer.

No, his memories must've been wrong, that couldn't be true.

He stood up, his legs shaking slightly as he was still waking up. The chains length allowed him to move 3/4th of the distance of the room. And at that distance, he could see the pictures.

And Papyrus was defiantly a Yandere for poor Sans.

All of the pictures were of Sans, every single one had Sans included somehow. They all had drawings on them, too. On every picture of himself, there was a bright red heart surrounding his face, drawn on by a sharpie. In the pictures that Papyrus was next to Sans, there was words scribbled on with arrows point at them, saying things like 'Together forever!' and 'He's only mine'.

This wasn't good.

At all.

The worst pictures were the ones with other people in them. Every other monster had angrily drawn scribbles covering their eyes and facial areas, sometimes even their whole bodies on certain pictures. There was the largest picture right next to the door, a group photo of Sans and all of his friends together they had taken after Frisk had talked to the King. Red scribbles covered their bodies, and three bold, black words were written over the red scribbles.

'KILL THEM ALL'

~~~~~~

Frisk took a deep breath, lightly knocking on Papyrus' front door.

It had been a day since Sans had went missing, and Frisk had spent the night crying. She liked Sans a lot, and she couldn't keep it all pent up. She needed to tell someone about it, and she chose Papyrus.

Something in the back of her mind told her this was a bad idea, but she ignored it. She just needed to get it out, and Papyrus was a good secret keeper. She always felt like he kept secrets pretty well, so she could trust him.

Right?

"Come in," Papyrus said lightly as he opened the door.

Frisk nodded and walked inside, awkwardly sitting down on the couch.

"I just need to say a few things, I won't be long," Frisk said.

"Go ahead," Papyrus said.

"It's just that, in the last couple of weeks, I've realized I really like Sans," Frisk admitted to the skeleton, looking off to the side.

"Oh, I see," Papyrus said coldly, a frown covering his face.

"I just needed to tell someone, it's been bugging me," Frisk continued, "And since he's gone, it's been pretty hard on me. I'm just worried that I won't be able to find him, and he'll stay locked up forever..."

As Frisk continued, Papyrus had walked up to the front door, clicking the lock on. Frisk stopped at the click, turning to him in confusion.

"Why did you lock the front door?" Frisk asked.

"I thought I had already killed all of my rivals," Papyrus said, approaching Frisk, "But I guess I have another to rid of."

She didn't even have enough time to react as a bone pierced her through her chest, blood exploding from her wounds. A choked cry of pain escaped her lips before she fell off the couch, twitching in her own pool of blood as her H.P depleted rapidly.

"You were always so annoying from the start," Papyrus tsked, crouching down next to Frisk and ripping the bloody bone from her body.

And that's how the final human died in the underground.

~~~~~~

"Ah, Frisk is later than usual, I'll have to go check on her," Toriel said, looking at the time.

All of Sans' remaining friends were gathered in Undynes house, trying to figure out who this monster was that kidnapped Sans. Toriel had set aside her hatred for Asgore in order to help, since she did too care about Sans.

So, Toriel had left, leaving the rest of them to their work. A knock on the door interrupted them all, making them all freeze. It was loud, pounding, and sounded desperate.

"Monster kid?" Undyne asked as she opened the door.

"Yo, U-Undyne!" The short monster said, trembling with fear.

"What's wrong?" She asked, him kneeling down to him.

"A couple of days ago, I-I saw Grillby walking through waterfall, and then Papyrus approached him and shoved him in w-with an attack!" He said quickly.

"Papyrus did what?" She asked in disbelief.

"I know what I-I saw, I ran and hid afterwards! He said something about Sans being his before he dusted Grillby!"

"Oh no," Undyne said.

"I-It was him?" Alphys asked in shock.

"We left Frisk alone with him!" Asgore panicked.

"Oh shoot," Undyne muttered, "We have to go right now. Kid, go back to your parents and keep them safe, alright? This might get ugly."

~~~~~~

"Ah ah, not so fast."

They had all rushed over to his house to confront him, only to find a scene in front of them.

Frisk was dead in the middle of the living room floor, her glowing red soul hovering above her corpse. Toriel was pressed against the wall, her stats floating next to her. She was down to one H.P, and a bone was at her throat, threatening to dust her away at every second. Papyrus was turning at the intruders with an insane look, everything they thought they knew about him gone in that moment.

They all stopped after running in, noticing the hostage situation in fornt of them. If they attacked Papyrus, he could kill Toriel, they wouldn't be able to save her fast enough. So, they just had to talk him out of it, or their ex Queen would dust right then and there.

"You guys found out way too quickly," Papyrus said, "I'm not really impressed, though. You guys have been bothering me and my love for too long, he's mine now."

"Papyrus, put down the attack, let's talk over a nice cup of tea," Asgore reasoned with him.

"There's nothing to talk about," Papyrus said, "Sans is mine, and you all are trying to take him away from me!"

"No we're not, w-we just want you to stop killing people!" Toriel coughed up some blood, clutching a wound on her stomach.

"No, no, no!" Papyrus said, clutching his skull, "Sans is mine, not yours!"

"P-Paps..." A voice said.

Sans stood in their doorway, a broken chain around his neck, the magic restraining bracelet still around his wrist. He took a glance at the others before looking back at his Yandere brother, determined to save his friends.

"Sans, you should be in the basement," Papyrus said, "You don't need to see all of this."

"I, uh... Just missed you so much, you hadn't come down!" Sans lied, smiling nervously at his brother.

"Really?" Papyrus squealed.

"Yeah bro," Sans lied, glancing over at his friends again, "I don't like it when you disappear like that, I want to spend all of my time with you."

"I knew it!" Papyrus said, clapping to himself, "Just let me get rid of these pests and we can live together forever!"

"Actually, Paps," Sans said, taking a few steps towards him, "Since Frisk is already g-gone, why don't we take her soul and use the others to break the barrier? Since Asgore is here, we can be together on the surface."

"What a great idea, brother!" Papyrus said, "I'll just kill them fir-"

"But the quicker we get there, the more time we can spend together!" The short skeleton quickly interrupted his brother, "Just leave them here, and we can go to the surface together. Forever."

Papyrus thought for a moment before looking at Asgore, Toriel, Undyne, and Alphys, telling them, "If any of you follow me, I'll use the bone to kill Toriel."

Toriel was surrounded by blue bones as Papyrus picked up Sans, giving a quick, "Nyeh heh heh!" Before he took the last human soul and ran out the front door.

Sans' head was on his brothers shoulder, giving off a sad smile to his friends as a farewell before he disappeared from view for good.