A/N, trigger warning, if you don't like gore, don't read the end of this chapter.

"Remember Papyrus. Stay with me. If we get separated anything can go wrong."

"Don't worry Father! The Great Papyrus will do the best job ever!"

Gaster and Papyrus stood in front of the newly repaired portal. Gaster had sent Alphys and Undyne home for the night.

"Are you ready to find your brother, Papyrus?"

"Yes!"

Gaster took a step behind Papyrus and smirked at a floating, transparent child in a bright green and yellow striped sweater. Blood started flowing down from the child's eyes as she shrieked with joy and flew into Papyrus's skull.

"Did you say something Father?"

"No, my son. Let's go find your brother."

Papyrus's dark eye sockets lit up blood red.

"Remember Chara. Don't make yourself known too soon. In order to truly take over this boy's weak will, you must make yourself out to be his own thoughts. It will be a tedious process and may take a while, but it is paramount to getting a new body for you."

"Hehehe, time for mayhem! You better uphold your end of the deal, WingDings!"

The possessed Papyrus walked into the portal with Gaster walking through several minutes after, when the hoodie was vaporized. This time, he put Papyrus's pet rock into the machine's Cross Dimensional Magic Locator. The portal lit up again and Gaster walked through.

<~>

Gaster reemerged on the roof of a tall building. He black, silk robes no longer covered graying. Ashy bones, but ashy, pale skin.

"I knew that would work. Hmm? It seems WingDings isn't possible with such a...fleshy human body."

Gaster summoned his Gaster Blaster, his bone attacks, and a thick, oily black goop.

"Good, my magic has transferred over nicely. Now, to find my...son."

Gaster let out a snicker and walked over to the roof exit. He walked down the stairs and into a bar-like room where a light blue haired man-child was griping about a, nomu? As soon as the few people in the room noticed the pale scientist, he was surrounded.

"Who are you and how'd you get here?"

A lizard looking monster in a mask held a knife in front of Gaster's throat.

"Pathetic."

Flicking his wrist, the goopy black substance dragged them all away from his person, leaving him to dust off his robes.

"Who the hell are you?!"

"My name is W.D Gaster. I have come to the wretched place to find my offspring, and maybe to do experimentation while I wait."

"Tomura, didn't the master say he needed a new scientist?"

"Yes."

"Bring him to me. And get him some proper attire."

A gravelly voice resonated through the bar, making Gaster's new eyebrow rise. He allowed the purple mist to teleport him to a restroom with a change of clothing and a mirror.

Dark gray hair; sunken, black cracks; light gray eyelights in an oily black void; ashy gray skin. Gaster's new human-esque body repulsed him, but he couldn't do anything about it at the present time. He dressed himself in a strange black, cloth robe that had to be tied. He left the restroom, only for the purple mist to fix his new robe.

"This is called a kimono. I take it, you're not from Japan."

"No, I'm not. Take me to your master."

Gaster walked behind the mist down an old, rusted wall to a room where an eyeless human was hooked up to countless machines.

"You may leave us, Kurogiri."

"As you wish."

The mist, Kurogiri, vanished, leaving the barely alive human lump and Gaster.

"Hello, W.D Gaster, I am All for One."

"Salutations. I hear you are in need of a new scientist."

"Yes. My last one...didn't follow orders."

"Pity. If you think I'm some lap dog, then you are sorely mistaken."

"No. You are a true man of science, and the father of one Sans W. Gaster, am I wrong?"

"That name is atrocious. His name is simply Sans. So you know where my incorrigible child is."

"Yes, he has taken up residence with a little family called Kirishima, and is in the Hero Course in UA High School. He is currently at the top of his class, in both school work and hero studies."

"Yes, my son was initially taught by myself. When he was...brought to this place, I assume this Kirishima family took my child in and enrolled him into the hero school."

"Are you interested in getting your child out of UA to learn here?"

"No. I think leaving Sans in that school will make him a stronger vessel for me in the long run."

"Elaborate."

"Sans was created by me for the sole purpose as a stronger vessel for my consciousness to take over. My current form will last for, at most, another few weeks. It is already deteriorating, so I will have to find a new, temporary form to take over, before Sans is ready. I will accept the open scientist position if you can provide a vessel that can last a few months."

"I see. Take your pick from this."

A clipboard fell into Gaster's outstretched hand as he looked over the many humans and monsters.

"This one. Haise Kai, quirk X-Ray."

"A grunt with a relatively weak quirk. One moment."

AfO pushed a purple button and Kurogiri appeared.

"Master."

"Bring me Haise Kai, immediately. He should be located in the Hassaikai Shie warehouse five."

"As you wish."

Kurogiri disappeared and reappeared with a lanky man with long, greasy, black hair and taunt, pale skin.

"Where am I?! Who the hell are you people?!"

Gaster smirked and forced both his and the man's soul to emerge. The man's soul was a deep burgundy; MALICE.

Gaster's smirk widened and fused their souls and plunged them back into the man's chest.

"I will be unconscious for a couple minutes during the transfer."

Gaster's old body melted into a goop and Haise crumpled to the ground. Slowly, the black hair on Haise's body grew lighter in color until it was a flawless white. His skin grew paler in color, his fingernail darkened to black. Gaster's silk black robes manifested from the goop and wrapped itself around Gaster's new body, as the wrinkled tee, pants, and sandals dissolved into black goop. The eyes snapped open to reveal two black voids with two white lights.

"That's better. This meat sack will last me a few months. Where is this lab, All for One?"

Kurogiri, lead him to the lab and give him the rundown on Nomu. The one at USJ was an utter failure."

<~>+<~>+<~>+<~>

Papyrus held his head as he rifled through Natsumi's medicine cabinet, searching for the human drug aspirin, to hopefully ease his headache.

"Pa~py~..."

"Hello? Human Eijirou, is that you?"

"No Papy~ I'm a little monster who knows what is good, and evil."

"Wowie! That's so cool! I'm going to tell Sans!"

"No! Sans won't understand, he'll take me away from you! You don't want to get rid of me, Papy, right?"

"Of course not. I won't tell Sans. What should I call you?"

"Call me Chlo. I'll help you decide what's right and wrong! We'll be the best of friends, forever!"

"Wowie! That'll be so amazing! I'm going to become what the humans call, a police man. It's like being a Royal Guard, but on the surface!"

"I'm so happy for you!"

Chara stayed out of Papyrus's ear until after they saw the panicked messages from Sans in the shared group chat.

"I hope Sans is okay."

"I don't know Papy. He seemed pretty scared. What if some meanie is bullying him?"

"No, Sans is much too strong for that Chlo."

"Maybe as a Skeleton Monster. He's a human now. And from what we've seen, humans are pretty weak creatures; with the only exception of the Great and Powerful Papyrus, of course."

"Sans being...bullied?"

"Whoever is being a meanie to Sans should face justice, right Papy? They could be beating him down, screaming disgusting, vulgar things at him. Are you going to let that stand?"

"No."

Papyrus's black eye holes flicker red for a brief moment before returning normal.

"Sans will tell me if he needs my assistance. Come Chlo! Lets go make our famous spaghetti!"

<~>

Papyrus watched as Sans descended the staircase dressed in a light blue t-shirt, black slacks, a white and blue flannel, and white sneakers.

"Papyrus, Sans going on a date isn't a great idea. When you have to go home, Sans will be too attached to this...HUMAN to go with you. He'll want to stay in this wretched place to be with his date."

Papyrus agreed, eyelight going crimson for a brief flash.

<~>

"Chlo. Sans went on the date."

"I saw. Don't worry Papy! There's still time to fix this! You still have to find your Dad right? Maybe he can help deal with Sans!"

"I hope so. In the meantime, all I can do is train to protect him. The stronger I can become, the more I can protect him!"

"That's the spirit Papy! I'll even share my spirit with you! It'll help you get stronger!"

"Aww! Thank you Chlo!"

Chara smirked and carefully fused his soul with their spirit, entirely. Papyrus slumped against the wall, but recovered with one eye completely red and the other normal.

"Did it work Chlo?"

"It did indeed my friend."

Over the course of a few weeks, Papyrus got quieter. More, rough with the suspects. More violent in general. There was one time he'd woken up in the kitchen holding a knife with a drippier version of his spaghetti sauce. Too tired to deal with it, he washed the knife and went back to bed.

When Sans got sik, and he had to take the vile human man to the station, he nearly impaled the man's through with his magic.

"Easy Papyrus. If you "punish" him now, Natsumi will suspect you of something. Best to wait for later."

"He is like the others. He is a disgusting piece of human trash Chlo."

"I'm more than aware. But if you're caught dealing with him, you won't be able to protect Sans anymore!"

"Fine."

Papyrus silently drove down the streets. His first kill had been entirely an accident. A woman who was criticizing Sans's unhealthy addiction to ketchup. He followed her as he walked through the woods with hiking gear and slit her throat from behind.

"OmTF, what have I done?!"

"It's okay Papy! She deserved it! She was bullying Sans! The whole point of us sharing a soul is so I can help you, and believe me when I say, she deserved what you did. Filthy human. Judging your precious brother for doing the things he loves! The nerve!"

"You're right Chlo. She didn't deserve her life, at all. I will continue to protect Sans. With everything I have!"

"Good."

Both of Papyrus's eyes bled with crimson light as he dragged the body to an abandoned cabin in the woods. Inside he had found several human corpses just rotting.

"Chlo?"

"You did this, remember?"

Papyrus did remember. He remembered killing dozens of people and stashing them here. Each and every one of them had something nasty to say about his brother. His regret faded into a disdain for the pathetic humans. He vowed that he would let no one get away with bullying Sans again.

<~>

"N-no more! Please, mercy!"

Cold, and moldy spaghetti was force fed to the disgusting human criminal whose very presence repulsed Papyrus.

"Mercy is not to be given to a filthy child predator who had his sights on my brother. Now, eat your spaghetti so we can continue our fun."

The man sobbed. He had been through days of none stop torture. The only times he got a break was when he'd answer his phone to talk to his family. He was supposedly on a fishing trip with a human he met at the market.

The breaks weren't very long. Only lasting twenty or so minutes. Then, it was back to scalping, the removal of finger and toenails, the peeling of skin, burning, stabbing, etc. The worst, is when the pale man would force gross and mold covered pasta down his throat. It healed him and gave him a temporary relieve from the pain, but his shock, pain tolerance, and mental damage was reset too, so he had to relive the torture every damn day until the man with red eyes decided to kill him.

The previous victims of Papyrus's wrath listened to the screams and sobs of the newest victim. They were glad they got a reprieve from their own torture, however brief. They knew when he was done torturing that man, their torture would return, but for now, they wait.

Vote, comment, and have a fantabulous day 💖💖😊😊 
2202 words  
Enjoy   

This chapter is dedicated to SpiritWolfNura. They have a great number of UT books. Two of which that I recommend, (because that's all I read so far)

Forgotten History, where the UT group except Sans, find a device in the Skele-bros basement that shows Sans baby-bone past from his perspective, super cute with baby-bone Sans 

and

One In A Million Stars (Blind Swap Papyrus X OC), where UnderSwap Papyrus was blinded in an accident with the C.O.R.E and doesn't tell a soul. Then he and all the other monsters move to the surface and a human girl, who happens to be an indepent, beautiful mentalist, see through his rouse. Her name is super cute, Nashira. How cute is that name?! 

Go check out these two stories. One In A Million is already completed and Forgotten History is still in the process of being published. They are both CRIMINALLY underratted, so please go show them some love.