Disclaimer: Naruto is the property of Kishimoto Masashi. The only reason I'm posting this here is because I actively enjoy courting flames. No, really, don't read this if you want to retain any modicum of respect for me.

Boys Will Be Boys

-x-

It was bound to happen sooner or later. Personally, Shisui would have opted for later. Or never. Upon consideration, never would have worked just fine for him.

They were on their way back to Konoha after a long but disappointing mission on the border of Suna, consisting almost entirely of mundane if not easily-dispatched tasks. Shisui felt that they had spent way too much time getting intimate with the elements, but tragically the warm bed he longed for was not to be had. The journey home was all grasslands and forests, but on the third night they'd stumbled upon a cave, saving them the trouble of having to pitch their tents. And hey, if they happened to disturb an irate bear of some kind, at least it'd instill some excitement into this uninspiring adventure.

If anyone ever asked—and he really hoped that no one would—Shisui would have to blame the hard tacks he'd had for dinner. He'd always found them slightly suspect, but evidently they contained some hidden pharmacological property that inhibited sleep even in subjects thoroughly wiped from a day on the trail. Frustrated, Shisui squeezed his eyes shut and tried to think of the most boring subject he could recall. Fugaku's New Year speech! That would put him in a coma in no time. He mentally began enunciating every monotonic syllable, reaching for sleep.

That lasted for approximately seven point five minutes.

The first thing he heard was a soft rustle of cloth. He dismissed it out of hand—sure, Itachi was a quiet sleeper, but even he had to shift around a little now and then. It was petty, but Shisui couldn't help the twinge of jealousy: they had both consumed the same blocks of concrete, but clearly Itachi's inhuman biology was effectively warding off their deleterious effects. Determinedly, he returned to the task of calling up in acute details the exact timbre of Fugaku's soporific voice as he had extolled the virtues of thoroughness in forensic investigation—

The next sound he heard wasn't quite as easy to explain.

It was not so much a sound as a series of little noises, slow and strangely slick, shaping the motion of something sliding back and forth. Something like, say, a wet tongue against skin. What the hell? Shisui boggled. Was Itachi licking himself over there?

Just as he was debating the best and most risk-free way to voice an inquiry, the noises came to a stop. Shisui would have gladly let it be, but he was now wide awake, ensuring that he did not miss the next rustle of cloth and definitely did not miss what came after that.

The slide of skin on skin was back, just as smooth and slick as before, except now there was something different about its frequency. More greedy and urgent. Familiar. Yeah, it was definitely familiar. There was a certain rhythm to this motion, an even slip-sliding, moving in one determined stroke after another—holy mother of fuck.

All the blood in Shisui's body instantly reached boiling temperature and rushed to his head. It had to be that. No way in hell he could be mistaken. Somehow, against insurmountable odds, his baby cousin had discovered the fine and traditional art of erotic self-stimulation.

Well there goes my robot theory, Shisui thought distractedly, but then experienced yet another heated full-body flush when he heard Itachi make a choked, half-broken noise in his throat. He was swallowing, hard, almost involuntary, the click of his throat obscenely loud in the still hush of the night. This was impossible. They were in a forest, for fuck's sake, it should not be this quiet. Quiet enough for him to make out with perfect clarity each of Itachi's quickened stroke, the slick slap of his palm, the subtle whisper when the back of his hand brushed the fabric of his pants. His rhythm was gaining speed, suddenly all jagged and sloppy—jerky, desperate, typical of someone who couldn't have been doing this for very long.

That much was apparent. It was clear, Shisui seethed, that nobody had given Itachi the So You've Discovered You Can Touch Yourself There talk that Shisui's father had subjected him to in his twelfth year, which, while traumatizing, contained the very vital instruction that such pursuits were to be conducted strictly in the privacy of one's room. Or possibly in the bath. In the bath, where he would be naked, all wet and flushing and hesitant, tentatively reaching one clumsy hand into the soapy water and down between his splayed thighs to grip his—

Itachi, lying a mere two feet away from Shisui, gasped softly and let out a hissing sigh, breathing it out through narrowly parted lips.

Oh my god, that's just not fair, Shisui growled to himself. The movements he could deal with, but did Itachi have to make noises while he jerked off too? Where the hell was all his stealth? Was he even a ninja? If he hadn't had the basic sense to go outside and touch himself where his only witness would be the tranquil night, the least he could have done was to make sure that Shisui had fallen asleep, or maybe cast a genjutsu over himself to conceal his illicit activity. Shisui direly wished he could cast a genjutsu on himself to block out this horrible reality, but that would require hand-seals and in this moment, even the slightest movement could prove fatal. Itachi's attention might be… elsewhere, but that didn't guarantee that he was any less of a paranoid hair-trigger basket case, and Shisui would not, would not be caught eavesdropping like some kind of sick voyeur. Even if Itachi didn't murder him for it, he would voluntarily strangle himself with his forehead protector.

In the horrifying silence of the cave, Itachi let out another pained half-groan. There was a crinkling sound, then a soft thump—he had heaved over onto his… back? No, face-down, all his sighs and moans muffled into the bedroll, and then there was—oh fuck—the slide of his small body against the cloth. Itachi was grinding into his bedroll, rocking his hips and thrusting into his fist. He had to be out of his mind if he thought Shisui couldn't hear that, asleep or not.

Shisui tried to keep his breathing even. He hated himself. Why did he have to be such a good shinobi? If he were more incompetent he would probably not even notice any of this. For that matter, why couldn't Itachi have been born a girl? There wouldn't even need to be that many alterations. Surely girls didn't do this kind of—on second thought, perhaps it wasn't a good idea to wonder what girls got up to, never mind what girl-Itachi would get up to. Sleep. He had to feign sleep. He slammed his eyes shut—a fat lot of good that was doing. With his eyes closed, he had virtually nothing to focus on but the images in his head, accompanied by the very real and very present sounds, which seemed to increase in volume in his blindness.

At this point, Shisui again experienced the unpleasant sensation of all the blood in his body rushing to his head—but not that head.

What the fuck? What the fuckity fuck? He had not spent all his Academy days fighting off plebeian taunts like, "I bet you get it up for your cousin," only to find out seven years down the road that he really did get it up for his cousin. He caught his lip between his teeth, hard enough to draw blood, and swallowed the coppery tang as quietly as he could. Flicked his tongue over the wound, then out and across his suddenly dry lips. Shivered. He was so ridiculously hard his pants were tenting—if he could just reach down, brush the outline of his erection, one touch, a little almost-friction or something, just to get some relief and, you know, not lose his mind. But he knew that if he did, it would be all over for him, and no amount of steely self-control would prevent him from shoving his hand down his pants as well and mimicking Itachi's every stroke and jerk. Best friends did everything together, right?

On the other side of the cave, Itachi was still moving. Shisui had had his back to him all this time, but he didn't have to actually look to know that Itachi was nearly arching off the bedroll, toes curling and stretching against the threadbare cloth as he fucked his hand. He was straining against the pressure of his own weight, driving his hips faster and faster. His skin was probably flushed, damp with exertion, his loose hair falling into his face and getting into his mouth. His breath was quickening, panting and gasping—he was so close, so, so close. Come on, you freak, just a little more, get this over with, please, Itachi, please…

With one last shudder, a sound halfway between a moan and a whimper, Itachi's body jerked in a quick succession of small thrusts, and then it was over. He sagged down into his bedroll and went still, going limp like all his bones had melted to water. Shisui opened his eyes, let out a silent, shaky breath. His body was still vibrating lightly; he had to force it to stop. Itachi was sucking in short little breaths lazily, quiet and sated and all but ready for sleep. Unbelievable. It was clear he didn't plan on getting up and going to clean himself or anything, so Shisui was just going to have to pretend to sleep in tomorrow morning to escape the mother of all awkward moments. He had a feeling he'd become an expert at diverting his eyes and becoming politely fascinated with inanimate objects by the time they reached Konoha.

Shisui clenched his teeth, and kept his hands fisted tightly in the rough fabric of his bedroll. He would wait, wait until he was certain that Itachi was asleep before getting up—just to be on the safe side, he'd even use Shunshin. It killed a piece of his soul to think that he'd have to resort to ninjutsu for this wretched purpose, but at least Shisui had the decency to seek solitude when he was seized by the need to get in touch with his inner self.

Eep! Don't report me to the popos, okay?