Papyrus sweated nervously as he watched in fear his younger brother think, the smaller skeleton sitting on top of him like a strangely shaped seat. He swallowed down apprehension, suppressing the begging plea to get Sans off of him, to apologize for going too far, to regain his dominance and-

"Souls are sensitive, right? The smallest touch can make a monster beg for mercy, the slightest burn could make them squirm in agony. What about the tiniest lick?" Sans asked, flashing a wicked smile that seemed to renew the memories of every nightmare Papyrus had about his brother. 

Sans moved his hand to allow Papyrus to speak, glaring darkly to give him a silent message that rebelling or screaming would not be permitted. 

"Sans, what has gotten into you?! I'm sorry for doing that, just let me up!" Papyrus said sternly, though his voice trembled. Sans picked up on it and rolled his eyes, the blue spheres of light as bright as ever, but with a dark twist. 

"What's wrong, Papy? I thought you always wanted me to act more like you." Papyrus narrowed his eyes, setting his jaw. 

"This isn't what I-"

"You are a sick monster, Papyrus. Trying to take advantage of me, while I was bound up like that? Despite my muffled cries for you to stop, and my obvious discomfort and inability to tell you no." Papyrus looked away at that, the guilt written clearly on his features. He didn't know what had come over him, he hadn't even tried to hold himself back. 

"I thought you were actually going to train with me.. That you were actually going to give up your day of sleeping and being lazy to teach me something, mentor me!" Sans said sadly, the hardened and angry look on his face softening. He rubbed his thumb over the surface of Papyrus soul gently, causing the older skeleton to shiver. 

"But I should have known better. That at any moment, anyone that I trust could turn on me without giving me a chance to react and use me. Now, I do know. And I guess we could say.. you will too." Sans' smile returned, as sweet as pie. Papyrus forced a shaky breath out, though it caught in his throat, his eyes widening, as Sans' grip started to squeeze his soul. 

"How's it feel, Papy? Don't be scared, I won't hurt you. Actually that was a lie. I just won't kill you." Papyrus' body tensed under Sans, obviously in pain as Sans pushed his finger tips into the orange soul, enjoying the way his brother scrunched his face, more sweat dripping from his skull. 

Papyrus felt like his bones were being crushed by an invisible force, expecting to hear the cartilage splintering at any second under the pressure. He tried to breath but it felt as if his chest was being held down, pressing the life out of him like water from a sponge. Tears leaked from his eye sockets as he closed them tightly, wishing he could scream as Sans squeezed tighter.

Then it stopped. 

Papyrus gasped weakly for air, shaking so badly that his bones rattled in their sockets, his soul even trembling. His breath hitched as fear washed over his mind, renewed when he forced himself to look at his little brother.

Sans just smiled. 

"Too much? Or perhaps not enough? It doesn't matter how much pain the victim suffers through, as long as the perpetrator is pleased." Sans studied the bruised life vessel in his blue gloves, noting the finger shaped indents in the mysterious texture.

"S.." He moved his gaze back to Papyrus as the monster tried to speak, smiling bigger at him.

"What's that, Papyrus? Are you trying to say something?" He waited a moment, watching Papyrus slowly breath, only having the slightest pang of worry that his brother might dust. After a few seconds of silence, he shrugged and looked at the soul again, wondering what he could do next. 

"That was a bit of a mean thing to do, now that I think about it.." Sans pondered aloud, a thoughtful look on his face. Papyrus would have flinched if he had the energy to do so, only able to close his eyes and fall limp. 

"Maybe it would be in the right place to treat you to something more.. satisfactory." Papyrus managed a faint croak, aiming to object, but he failed. He jolted with shock as an anomalous sensation of warmth seemed to wash over him. His breath quickened as the shock quickly turned to arousal as it continued, supplicating him to conform to it's alluring spell. 

He could feel himself lifting his back, arching as if he could get feel more of the sensation, so wrong yet so right. He shivered and let out a soft whimper, emotions and pleasure conflicting in his mind. He didn't know if he should feel pitiful or pleased.

"Like that, Papy?" Sans asked in a sly tone, smiling as Papyrus looked at him, the taller skeleton's face turning bright orange as he realized Sans had been licking his soul. Papyrus pressed his spine back to the floor, watching a thin line of saliva connecting Sans' tongue and his soul fall and break apart. He felt Sans' breath warm him. 

"N-"

"Shh, you can't lie to me. I can feel your soul throbbing with your pleasure. It's humming. You can't hear it, but I can feel it. Almost.. Vibrating with enjoyment." Sans giggled when Papyrus' cheeks flushed more, heated as if his skull was on fire. He hoped Sans didn't take notice of the new, hard ridge in his shorts, in between his hip bones. 

"I see why you didn't stop." Sans commented, talking between tiny laps with the tip of his tongue, creating the image of hot hands dragging across his brother's body in Papyrus' head. He smiled at as he heard another soft groan. 

"It's too much fun." Papyrus gasped and barely managed to cut off a pleasurable cry as Sans sucked at his soul, gnawing ever so gently with his teeth at it's side. The burning warmth continued, now ignited with a heavier rubbing sensation. Small nips sent pain through Papyrus' bones, but still added to the euphoric hedonism, lined with moans. 

Sans giggled and kept up his naughty act, watching every way Papyrus moved, listening to every sound Papyrus made, feeling his own excitement stirring. He caught a glimpse of a blue luster in his pants. 

"Papyrus.. keep doing that.." Sans whispered lustfully, growing needy and impatient, his nibbling and licking losing it's tenderness, replaced by desirable urgency. He started to move, panting softly as the motion stirred the fabric between his lower regions and Papyrus' torso, which in turn had Papyrus breathing heavier and getting louder. 

"Sa.." He murmured, yelling softly as Sans bit on his soul. He felt his skull become slick with sweat, the sensations building up to something out of reach, to which Papyrus would stop at nothing to feel. He moved his hips up, successfully guiding Sans back so that the smaller monster's tail bone rubbed against his member. 

Sans didn't take notice until he grinded a little harder, feeling something push against his back side, seeming to fit perfectly as his pelvis locked into place with Papyrus', his member just above his brother's, separated by their clothes. 

"W-wait.. No.." Sans tensed his legs and forced himself up so they were no longer in contact, pulling Papyrus' soul out of his mouth. As they lustful fog that had clouded his mind and actions dispersed, so did Papyrus' pleasure, who let out a long, upset whine. 

"No, no you can't do that.." Sans said slowly, beginning to frown and in turn glare, straightening so he stood above Papyrus. The older monster panted, drool dripping from his mouth.

"You don't get to do that." Sans remarked, almost disgusted in himself from nearly letting his brother get his way, when it was clearly his turn to be in charge. He got to say what they did, and what they didn't.

"You're not getting me, Papyrus. That's wrong." Sans scowled, subconsciously bringing his hands closer to his chest, as well as Papyrus soul, glowing brightly, the light sort of distorted from saliva and bite marks across the surface.

"But.." Papyrus let out an uncharacteristic whimper, sounding so strange that Sans froze momentarily, taken aback. He'd never heard his brother sound so.. so.. biddable. 

"You.. started.. you.. finish.." Papyrus said meekly, turning his face away to catch his breath. His arms were laid out and limp, his wrists scraped and damaged from moving around in the makeshift bone restraints. Sans' gaze roamed his brother's body, incapable of straying away as they met with the orange luminescence beneath brown fabric.

"This is so disgusting.." Sans muttered, slowly lowering himself back down into the nearly welcoming presence of his brother's member, seated perfectly above it, if not for their clothes, it would.. he pushed the thought from his mind.

The heat from Sans' magic near his pelvis stirred Papyrus' lust, as well as his soul. He let out a subdued groan as it flashed and hummed in Sans' hands, without sound, feeling like a cat would when purring. 

"W-woah.. Papy.. your soul.." Sans whispered, newly captivated by the mysterious and strange vibrations running through his fingers. It wasn't enough to be seen, but enough to be felt. His mind slipped to an idea that made his own soul sink, though he followed through. 

"This.. this should be.. cl-close enough.." Sans had lost the threatening and stern personality that had taken him over, once again replaced by innocence and timid behavior. Papyrus managed to look over just in time to see Sans' face, pointed down, brighten blue, with hues of orange. And not because he was blushing.

"Wh- Oh.. oh stars..!" Papyrus sharply called off a yell as he once again was plunged into the warm and moving sensations across his bones, this time influenced by the knowledge of what Sans was doing to create them. 

"I'm sorry, I'm sorry!" Sans squeaked, his shoulders stiffening and trembling as he tried to focus on his task, his grip on his mind slipping, overcome with newfound pleasure. He whimpered and moaned in time with his brother, his finger tips slipping against his member. Papyrus' soul pressed between his palm, and his shaft. 

The soft throbbing hum produced a feeling unlike Sans had experienced before, even better than his hidden and secret assemblage of naughty toys. It was subsided enough to barely be noticed, but vivid enough to create a new feeling all together. 

He moved his hand against his member in a stroking motion, barely capable of keeping Papyrus' soul to it. After a slip up and nearly stopping the pleasure, Sans didn't stop himself from sliding his other hand into his pants, rubbing faster.

Papyrus shook violently, his face scrunched and orange, saliva pouring from his open mouth. His breathing was cut off by loud groans and shuddering gasps, matching Sans' noise perfectly. He could tell he was getting closer to the intangible objective, that need that he had to fulfill. He couldn't be held down any longer.

"Papy!" Sans cried out as Papyrus broke the bones over his wrists and embraced him, the older skeleton's arms squeezing his body tightly to his brother's chest. He yelped as Papyrus pushed him down against the floor, moaning as Papyrus thrust against him, forcing his hands to move faster on his member.

Papyrus yelled as he hit his climax, a warm liquid like substance collecting on the front of his shorts. His body gave up on him and he fell ungracefully off of Sans, onto his side on the floor nearby. 

His soul flashed brighter than Sans had ever seen, the magic build up finally released and pulsed through Sans' member, pushing the small monster to his limit. He screamed as he finished, cum collecting on his shirt and the soul, already mixed by other fluids. 

Sans' energy and strength drained too quickly, his body convulsing as the effects of his orgasm crashed hard into him and knocked him unconscious, sprawling his limbs across the floor as he fell back into the advancing darkness. 

(I don't know if I like how this turned out, but hopefully you readers liked it)