Post-Pacifist

The space ship slowed and gently set itself down on a rocky outcropping of Mt. Ebott. Frisk and Sans exited the ship walking over to the cave entrance. As it turned out, there were many caves in Mt. Ebott, but there were only two leading to the true Underground which the monsters had left three years earlier.

"so, this is the last place. to be honest, kid, i didn't expect this day to ever come. or any of this to happen, really," Sans said as they both stood there. Frisk remained quiet allowing the skeleton to speak his mind. Through their years spent together, they knew he always appeared to carry a heavy load on his mind.

"i'm a little worried about going in there. i mean, being split into dozens of pieces and being suddenly put back together. what would you do?"

"…"

"you're right, kid. we won't know anything until we go in there. don't be afraid. i'm right behind ya," assured Sans giving Frisk a complementary wink. They shifted the backpack they were carrying on their back and walked inside the cave known as Cave of Echoes.

It wasn't dark at first, but quickly the light of day and the hum of the space ship disappeared. Frisk couldn't hear Sans' footsteps, but they knew he was following. He preferred to be kind of secretive about it was all.

The cave began to have a familiar blue glow when Frisk rounded a corner. They saw the path extended into a cavern covered in echo flowers kept alive by a pool of water. The flowers repeated the sound of their footsteps. This beautiful, nostalgic sight became cut short by a sudden bright flash of light.

At the end of the small cavern a grey door appeared fixed to the wall. Frisk walked over and turned the knob their determination too strong for any sense of caution. They found the room inside a stark white and empty except for a formless black orb.

Frisk took off the backpack taking out of it a similar, but bigger, black orb. It began to levitate and floated over to the other orb fusing together. Another bright flash followed causing Frisk to wince.

They saw standing in the center of the room a skeleton dressed in black. He had Papyrus's slender and tall stature, but the smile on his face closely resembled Sans' own. As he looked around with drooping eyesockets little black specks fell off of his frame. He caught sight of Frisk and the smile dimmed.

"ah, so you are the one who…put me back together…" Gaster's voice sounded harsh and rusted from disuse. He attempted to clear his throat and speak more clearly, but it didn't helped much. "Then I apologize, human, for what I am about to do. It was nice meeting you."

Suddenly, Frisk was pulled into a fight.

"But you cannot be allowed to exist."

Frisk watched as Gaster's eyes swam with blue and orange magic. From behind him large circular voids opened and huge, unfamiliar skulls appeared out of them humming with energy. Frisk dodged the blasts of magic they fired at them. Next there came a barrage of bones, and they barely managed to get all the movement combinations correct.

"Hm. You see, human, I have seen all the harm you could have done. All the resets you could ever make. All the routes you could take."

Frisk used that moment of dialogue to catch their breath before another barrage of bones. These were more fierce than the ones they encountered long ago with Papyrus. Frisk could see the skulls hovering close by Gaster's side waiting to be used very soon.

"Letting you live would put everyone at risk. If I know the truth, why let you be if I have the power to take your soul?"

As Frisk predicted, the skulls came at them firing no longer solitary blasts but short, strategically angled ones. They decided to act, to plead their case to Gaster because Frisk knew of their power to reset. They remembered taking an oath not to use it ever again.

"Hmpf. Your words are empty to me, human. I see you only as a threat."

Gaster's eyes changed to purple, and Frisk felt a familiar tug on their heart. It was as if it had been strung up by an invisible thread. Gaster spoke again after they managed to survive the attack mostly unscathed,

"Spider magic is rather easy to learn once you've seen it a few hundred times. Can your resilience last?"

Frisk dealt with not only the spider magic, but another bone assault ending up bruised in the process. They could feel Gaster's resolve to kill them and keep this timeline safe. It distinctly reminded them of those fights from years ago.

Frisk had to take action again. This time they called for help.

"You were followed? Of course you wouldn't be able to find all traces of me without help. How silly of me."

The door to the room became devoured by a circular black void. Frisk felt a sense of dread travel through their body down to their very soul. Gaster had so much power, how would they win without the others?

Frisk took a deep breath. The others would find them. Even if their determination served as the only spark of light in the void Gaster might throw them into, they would be found again.

"The look on your face… That is your determination? In person it does suit you well. Now perish."

Frisk felt the thread disappear from their heart and be replaced with a heavy weight. Bones and blasts were thrown their way, not haphazardly, but with surgical precision. At the end of the bout, Frisk was panting and heavily bruised. The weight on their heart seemed to grow heavier as they realized what might have to be done. Something they remembered resorting to only once before.

Gaster raised a skeletal hand when suddenly Frisk was tugged backwards. The void blocking the door broke like glass, and the grey room opened up into the cavern of echo flowers.

The sound of shattering glass echoed around them briefly before a voice silenced them.

"Sans."

"well, this wasn't the reunion i was promised," said Sans dispelling his magic. Frisk stood in front of him and saw on either side Undyne and Toriel. Both of them looked prepare to fight.

"We're here for you Frisk, just like we promised we always would be!" Exclaimed Undyne a spear already in her hands.

"Come here my child. I will heal your wounds," spoke Toriel summoning her healing magic in her hands. She proceeded to guide Frisk out of Sans' way.

"[Sans, my son, what are you doing?]" Gaster spoke in a language Frisk didn't recognize. His face became clouded with disappointment as he locked eyes with the smaller skeleton. They could see magic still danced in his gaze. It wasn't dreadful to look at with the others there.

"it's been a while since i talked like that. you might have to repeat yourself," Sans paused as Gaster looked ready to do just that when he broke in with, "just kidding, i heard you the first time."

"Sans, you know what they're capable of doing."

"yeah, you think i didn't know? i practically lived with that for years. i also wasted a lot of time sitting around trying to work on the machine you left me. all those times i had dreams about you. how could i forget all that?" Sans paused again to collect himself. "the reason i went through all this trouble to bring you back was because of Frisk. living with them, and talking with them, i realized the only thing missing when i got here to the surface was you."

"so dad. please. stop with the fighting and come home," Sans pleaded holding out a hand. Gaster stared at him as the echo flowers whispered the last words. Come home… Come home…

Gaster looked from Sans' face over to Frisk who was mostly recovered and standing on their own. He looked back at Sans and heaved a sigh. The floating skulls disappeared back into their respective black voids. The magic disappeared from his eyes. The smile appearing on his face conveyed how tired he looked.

"It's been so long since I heard you ask me to come home." Gaster spoke in a gentle tone the rusty quality gone for the time being. He walked over and clasped Sans' hand with both of his own.

"yeah…too long you could say," Sans replied looking up at his father with his usual smile. They remained like that for a few seconds before Gaster pulled his hands away to look at the others.

"Where are my manners? Allow me to introduce myself. I am W.D. Gaster the former Royal Scientist for the kingdom of monsters." He looked down at Frisk the smile gentle now. "I thank you for being such good friends with my sons."

Toriel did a polite sounding ahem and, after catching her eye, Gaster continued with, "And I apologize for my outburst of anger."

Frisk returned the smile and said it was okay. They understood why Gaster would go out of his way to do such a thing. So many monsters had done the same.

Undyne pointed out they should probably get back to the ship since Papyrus and Alphys might be worried about them taking too long.