Robin paced along the side of his bed in his quarters, safely separated from the barracks he shared with his companion fighters. On the bed itself sat the object of his consideration, perched cheerfully with one knee pulled up beside him, resting his weight through his hands on the ankle of that leg.

Oh, Shulk, Robin thought, tilting his head as he admired the other boy, Don't look so cute and innocent like that. It makes me feel worse for roping you in to my filthy games like this.

Out loud, he only said, "Thanks for dropping by, Shulk. I was glad to see you accept my invitation on such short notice."

"Of course I had to come!" Shulk chuckled, beaming. "When you said you wanted my help with an experiment, it was the least I could do. You've seen tons of my own experiments in the lab."

"This one's a little different," Robin muttered, though he remembered fondly the numerous interesting machines Shulk had built and glowingly shared with him. To one like Robin, who had had no prior experience with machines of any sort, even the simplest gyroscopes that only whirred and spun were fascinating new marvels to him. He lacked the ability to understand how Shulk constructed such things with his own hands, and admired him for it.

The experiment he wished to attempt today was nowhere near so admirable.

Shulk seemed to catch on, perhaps detecting Robin's heat signature rising. "Is it... a sexy experiment?" He leaned forward as he asked, brilliant blue eyes wide.

"Well, yes, it is," Robin confirmed, allowing a smile to tug the corner of his mouth.

Shulk brightened even more, his own smile overtaking his features. "What are we waiting around for? Every second is a second wasted! This is for science!"

Robin silently thanked every God he could think of (some of which he knew personally) for the insatiable sex drive of youth.

Within minutes, encouraged by Shulk's enthusiasm, they determined to set things in motion. "In this experiment," Robin explained, helping Shulk out of his clothes, "I won't be touching you after the initial setup, and to disallow you from touching yourself as well, you must be restrained. May I tie you?" Shulk, curious and eager, nodded. Robin had produced a length of soft silk, and Shulk allowed him to hold his arms behind his back so that one forearm rested on the other, and tied them together.

"This is a little... well, kinky," Shulk tested the restraint, smiling as he found it not too uncomfortable, heat already coloring his face.

"Yes, it is pretty kinky," Robin smiled, too. "I thought that if I'm to practice this sort of experiment on anyone, it ought to be you."

"I am honored that you thought of me," Shulk said with mock pride. "All right, kinky experiment is go."

"Please remember, however," Robin urged, shrugging out of his own robe and hanging it near the door. "If at any time you want to stop, the word is 'pause.'" Shulk giggled, doubting there was anything Robin could throw at him that would make him want to stop, but grateful for the thought of his safety all the same.

Shulk was situated on his knees on the soft quilt comforter of Robin's bed, naked and wrists bound. Robin had produced a pretty crystal jar, its edges beveled like a cut diamond's sides. The jar was filled with a creamy balm, which Robin scooped a small amount of with his fingers. "You'll like how this starts," he promised Shulk. "First, I get to massage you." He was rubbing his hands together to coat them with the balm, and leaned in toward Shulk, resting one knee on the bed for balance.

It was a slow, sensuous massage over his erogenous zones, something both of them simply enjoyed in the quiet for a while. Robin enjoyed the soft handfuls of Shulk's butt, enjoyed trailing his fingers down the crevasse, giving his hole a little swirl so that it was covered with balm as well. Shulk tensed and relaxed, closing his eyes as he let Robin's hands explore him.

Working from the front and with a new slathering of balm, Shulk's inner upper thighs were massaged next. "It's surprisingly warm," he observed, in part to distract himself as Robin gently handled his balls.

Next, Robin had the pleasure of feeling Shulk hardening in his hands as he rubbed the balm lovingly over his cock. It was not much unlike lubing him up, although the consistency of the cream was different.

"Now, how is this different from any other 'experiments' of ours?" Shulk asked playfully of Robin's apparent handjob, grunting through the sensation.

"Oh, just wait and see," Robin promised, and just to punish Shulk's impatience, he paid special attention to the folds around the head of his cock, even rubbing the balm over the very tip, cruelly applying pressure there with his thumb. He was satisfied with the louder grunt Shulk produced in response to the tender stimulation, watching with fascination the contraction of his stomach muscles. Inspired, he coated some of the balm there, too. As tempting as it was to continue here, Robin didn't want Shulk too stimulated before the trial even began, so he retreated to move on to the next part.

"All right, one final step in the setup phase," Robin was close to his face now, a tiny bit more of the substance on the tips of his fingers, which he held near his mouth. "Open up."

"Is that stuff safe to ingest?" Shulk questioned, unsure.

Robin bit back his tongue to hold back the words, That's what we're going to find out, and said instead, "I would never put you in any danger." His fingers went deep into Shulk's waiting mouth, coating the back of his tongue.

Shulk closed his eyes and lapped it up. He was surprised by the flowery flavor. He wished he had greater knowledge about plants and herbs, so that he might guess at the effects all this might have on him. He thought of perusing Robin's bookshelf for a plant life encyclopedia, distracted by the enticing thought of learning something new, but came back when Robin began to retract his fingers.

As Robin pulled his fingers out, Shulk playfully sucked and licked them. His eyes opened and he did not break eye contact with Robin, gazing at him lustily as he searched for every last drop of the substance with his tongue. Robin beamed, thoroughly aroused, thinking, Oh, I could not have picked a better person for this.

It was with some difficulty that he retreated from the bed, leaving Shulk on his knees there. "Tell me about everything that you feel," he instructed, twisting the lid back in place on its jar. "It should be kicking in soon."

"It's getting warmer already. I mean... where you rubbed it," Shulk blushed a little. Then he asked, "This isn't going to burn or do anything painful, is it?" Truthfully, he was feeling a small amount of trepidation about having the unknown substance on his most sensitive areas.

"It shouldn't," Robin assured, "But if it does get too hot, please do not hesitate to say 'pause.'"

"Right," Shulk nodded, comforted.

Soon, Shulk began to feel a change in the effects of the balm, in addition to the heat. He turned his head, attempting to place what he was feeling and put it into words for Robin. "It feels... like some kind of movement, sort of," he attempted, hoping that didn't sound weird. It was a stimulating sensation, and his own breathing involuntarily grew heavier. He felt sensitive parts of himself twitch in response. He leaned over, folding over his crotch, wishing his arms were free so he could further stimulate those areas, but he could do nothing but resign himself to the effects of the balm. It washed over him in hot waves, seeming to simulate pressure and movement. Some of it radiated from his asshole, where Robin had coated a heavy layer, and traveled over his balls, all the way up and back down his cock. The very tip felt to be another radiating point, the origin of the waves that pulsed up and down his shaft, concentrating where he was most sensitive. He felt the waves extend over his thighs and stomach as well.

Shulk's hips bucked, an involuntary movement. His breath came heavily, his face and neck flushed deep red. Robin observed the strain on his member, thick and hardened with want, already dribbling from the tip. Another thrust, this one accompanied by a helpless mewling cry.

"R-Robin," Shulk managed, struggling to form words through the combination of labored breathing and mental fog.

"Yes?" Robin was ready to leap in the moment Shulk asked to "pause," but the request never came.

"I need... hah... would you... touch me? Anywhere... I need... hihh... I need something..."

"Sorry," Robin apologized, hiding his amusement, "The experiment specifically calls for your reactions without any outside interference. But, tell me, what is it that you need?"

"I... need... something, anything, in my..." Shulk couldn't seem to form the word, but he arched his back, perking up his backside, begging for stimulation beyond the sensations the balm supplied.

"Your what?" Robin smirked.

"My ass, God, I need to be touched there, even if it's just your fingers, I – ffffffuck," he bucked again, giving a helpless, high little bark. Robin fully absorbed the luscious sight of the young man completely unraveling before him, using vulgar words he'd never uttered before.

"I have to... fuck... please, would you... my cock, please, I've got to fuck something," his voice trailed off into a high whine as he bucked rapidly at nothing, his rigid cock twitching and pumping out more viscous liquid.

"Perhaps next time," Robin said, pretending to rest his hand on his chin in thought, but in fact masking the deep blush that crawled over his face. "This first run of the experiment must serve as the baseline for further tests." Shulk moaned long and loud at that, only half in disappointed response while the other half was simply the loss of control over his voice. His body was wanting, but not getting, and that denial fueled the wantall the more.

"Ah, I know something I can do," Robin realized, picking up the jar again.

"Wh-what?" Shulk heaved, eager for Robin's touch anywhere on his overstimulated body. Leaning onto the bed again, Robin rubbed some balm between two fingers, then over Shulk's nipples, the contact on such an erogenous zone making him gasp and whine. But then Robin backed off again, leaving Shulk without the stimulation his body begged for. It activated quickly, and Shulk cried out as the heating sensation overtook his nipples, erect and sensitive to every wave the substance pulsed out over them.

"Ah, hah, hah," Shulk's voice was nothing more than high, airy breaths now, as his entire body bounced on the bed, high on his knees in response to an invisible assailant that accosted his ass, his thighs, his bouncing privates, his throbbing cock, and now his perked, sensitive nipples as well. Observing all of this, Robin's own breathing had grown a little heavy, too. He felt some want of his own. He wanted to move forward and get his hands all over Shulk's begging body, and take that hard, thrusting cock in his hands or mouth, and cover his gasping, open mouth with his own. But he held back in a fantastic display of self control.

Shulk's desperate movements grew even more frenzied as his eyes shut tight, tears forming at their corners. Under Robin's awe-stricken gaze, after many more moments of listening to Shulk's high, breathy moans, the back of his throat released one final squeak as his back arched and his eyelids fluttered. In that final thrust, cum spilled from his straining cock as veins bulged along its length, the liquid running in rivulets down the shaft while a few loose globules splat onto the bed. Shulk's back held him in that arch for several moments as his cock unloaded a few more spurts, then his shoulders slumped forward and his knees gave out, falling back to the bed in a weakly sitting position with a deep, relieved sigh.

Robin still absorbed everything he'd just observed, mentally replaying the scene with the hope of committing it to memory. He gave Shulk a few moments to catch his breath before moving to him, joining him in sitting on the bed. He tugged at one end of the silk that restrained Shulk's forearms to untie it, his arms simply falling limply to his sides. Robin tenderly brushed back the blond hair from Shulk's face, finding the roots soaked with sweat. Just as he began to caress the young man's tired face, Shulk surprisingly closed the remaining distance between them, devouring Robin's lips in a ravenous kiss.

With wet, open-mouthed motions, he was kissed over and over, Shulk's tongue lunging deep inside his mouth. Robin was perfectly content to take these deep kisses, thinking of it as the other young man taking out his frustration on him, so to speak, but suddenly he recognized a new, unfamiliarly sweet taste on Shulk's tongue. "Ah! Wait!" he pulled back immediately, explaining, "The balm! It can still... activate..."

"I thought it might," Shulk grinned, using his new vantage point to slip the silk around Robin's wrists while he had the opportunity of surprise. "Your turn."