One.
The spell had been meant for Potter and Sirius, but they had been alerted a split second before Snape and Mulciber had got off their spells by the sound of Rosier cursing as he stumbled (over his own large stupid feet). Regulus had been behind them, wand drawn and watching as all hell broke loose. The next instant Lupin's wand was out and before Rosier could regain his footing he was laid out on the floor, rigid as a statue.
Sirius and Potter had split and flanked them, firing hexes rapidly at the standing Slytherins. Pettigrew had ducked behind a suit of armor and shot a volley of wild furnuculus hexes down the corridor. Approving of this strategy, Regulus had taken refuge behind another suit, though his ensuing hexes were much better aimed.
Everyone else was dodging and ducking, shouting instructions, and trying to shake off the effects whenever they were grazed by a random spell. All in all, it had turned out to be a major cock up.
A jelly-legs/langlock combination took Mulciber down, then Rosier went tap dancing down the hall. Sirius, who never could resist a chance to gloat, had laughed, puffing out his chest and taunting Snape.
"Had enough, Snivellus?"
Before anyone could react Regulus had fired the spell at his brother knowing Snape would stick to the plan despite Sirius' taunts. He would never pass up a chance to hex Potter, Sure enough, Snape had pivoted sharply and cast the spell.
"Protego!" Lupin had yelled, throwing a bubble of protection over Potter, while his brother cast his own shield with an insolent flick of his wand. Both spells had ricocheted, careening in opposite directions like billiard balls, from stone to armor and shooting with full force into Lupin and Regulus. They had both gone down like sacks of flour.
Regulus didn't remember the teachers showing up, nor being levitated to the infirmary, nor being out cold until the next morning when he finally woke with the worst pain in his head he'd ever felt. He groaned and reached his hands up to steeple his fingers against his temple and rub at them in a futile effort to lessen the pain.
"What did you do to him?" his brother's voice hissed. Regulus rolled his head to the side and saw Sirius sitting in a chair next to a bed where Remus Lupin was laid out. "Snivellus said it was just a modified stunner gone wrong, but I know he's lying."
"I have no idea what you mean," Regulus said, saying the first thing he could think of to deflect the question. He needed time as he felt he could barely string two thoughts together. The spell-that was it-they had cast it and it had misfired and-
"Bullshit," Sirius spit. "I want to know now what you did."
Unfortunately, Regulus was probably more afraid of the answer to that than Sirius would be.
"My head is killing me," he stalled. "Where's Pomfrey?"
"Serves you right, you little toerag. If you don't tell me what-"
"Do I hear voices?"
The sound of Madam Pomfrey's footsteps echoed and Regulus rolled his head again to watch her stride toward his bedside. When he looked over again Sirius had disappeared.
Pomfrey spent several minutes checking him over before giving him a potion for his head and telling him he should rest a bit longer in the infirmary before returning to his dorm. Sirius didn't return and Regulus, his headache receding to a dull throb, ended dropping off to sleep again.
The next thing he knew his eyes popped open and he shot straight up in bed.
"What the fuck?" Regulus' voice sounded in clipped, astonished syllables, simultaneously mirroring Remus Lupin's thought inside his head.
Regulus snapped his mouth closed and looked around. The infirmary was empty except for Remus Lupin's body which remained supine on the bed next to him.
What? What is this? Lupin's thoughts were frantic now. Why am I-
Calm down, Lupin. Regulus winced at how loud the thoughts seemed to ring. There is a perfectly reasonable explanation for this.
Silence for the space of five seconds, then-
Regulus? Lupin's voice, thoughts, whatever, sounded incredulous.
"Yes," he whispered, unnerved by carrying on a conversation solely inside his head.
What happened? What did you do!
"It was a spell obviously. Meant for Potter and my brother. Everyone always says they share one brain. We thought it would be funny if they literally did."
Oh God. Is it-is it permanent? Lupin was getting hysterical. How is this even possible? Can you end it?
Regulus did, of course, know how to reverse the hex, but he wasn't sure he was ready for that yet. It might benefit him to observe the effects a while longer. No one else knew what had happened. Not even Snape. He could keep it to himself and maybe use it to his advantage.
Well!
"I can."
Regulus could feel the relief, quite pleasant actually, seeping through his thoughts, spilling over into his emotions. He smiled.
"But I'm not going to yet."
Two.
Lupin had been furious, had argued with him all the way back to the dungeons. He'd only shut up and listened while Snape had quizzed him over what had happened. Regulus had insisted the hex had gone wrong and he felt perfectly normal, and he told him that, no, Lupin still hadn't woken up. Then he had escaped to his room.
He went on with his daily routine. He ate lunch and dinner in the Great Hall where his brother and Potter glared daggers at him across the tables, either ignoring Lupin's incessant harassment or prodding him in turn. He sat in the common room and pretended to read as carrying on a conversation with someone other than Lupin was proving difficult.
The whole experience was very odd. They couldn't read each other's thoughts unless it was intended, equivalent to the words being spoken aloud, but there was more than a faint tinge of emotion that seemed to leak through consistently. From what he could tell, Lupin's predominant mood right now was murderous. In any case, it was tiring, and when it was late enough to be reasonable, Regulus took himself off to bed.
As he stood in front of the mirror to brush his teeth, he wondered how it was to look out with what felt like your own eyes and see a completely different person. Regulus spit and rinsed and then straightened, smirking at the mirror.
"Like what you see, Lupin?"
What I see is that vanity is a commonly shared Black trait.
Regulus laughed.
"You know Snape insists that you and my brother are shagging. Potter, too, for that matter."
Quite. We haven't heard that one before. Lupin's sarcasm came through loud and clear, and Regulus smiled wider.
"I don't agree with him. I know my brother, and I know he's not shagging blokes."
He could feel something then, something niggling on the edges of that emotional pipeline they had, but the finer details eluded him.
"Snape says you watch him all time-my brother."
And there. Definitely something there. What was it? Fear? Shame?
Regulus put his palm flat against the mirror and leaned close, opening his eyes wide. He knew how much he looked like Sirius. Under certain conditions they could almost pass for twins, barely a year's difference between them.
"This is your perfect opportunity to take a good look, Lupin, without fear of being caught."
A burst of shame, anger, denial flared briefly.
Shut your mouth, Black.
Regulus laughed.
"All right, then, whatever you say."
He wasn't sure what prompted him to do what he did next. Just the idea of messing with Lupin, and with his brother in a roundabout way, was suddenly very appealing. And so very easy. He stepped back, allowing a fuller view of his body and stripped off his clothing piece by piece. When he was naked he stretched, admiring the flat planes of his stomach, his smooth pale skin, and his cock, which even flaccid was thick and straight and as impressive as the rest of him. Then he turned and twisted slightly to look over his shoulder, providing the still silent Lupin with a magnificent view of his back side. When he had given him a good long look, he wished him a seductive goodnight and slipped between his sheets naked.
Three.
The next day was Sunday and Regulus woke early to avoid his housemates and to have an early breakfast in peace. He had the Great Hall to himself until his brother came in looking haggard, as if he hadn't slept all night. Potter and Pettigrew were with him. They must have been visiting Lupin's body in the infirmary.
My brother doesn't look so good with bags under his eyes, does he? he taunted Lupin. I wonder whatever could be keeping him from his beauty sleep.
A flare of worry came from Lupin then, and on the heels of it, anger.
Temper, Lupin. You wouldn't want me to accidentally point out to my brother how enamored you are with him, now would you?
Bastard. Lupin's thought slides into his brain with a painful spike, but Regulus calmly folds his napkin and stands, making his way to the Gryffindor table.
"What do you want?" Sirius snarls and his hand goes to his wand.
"I just wanted to say good morning, brother." Regulus smiled. "And ask how your little half-blood is doing."
Sirius shoved back from the table and fisted his hand in Regulus' robe. Out of the corner of his eye he saw the other two stand, as well. And then things went wonky.
"Sirius!" Regulus cried, throwing his hands up and pressing them against his brother's chest. He could feel his eyes widen in shock. His reaction or Lupin's-he wasn't sure. Lupin had just spoken, had used and moved his body and Regulus hadn't even had a chance to stop it.
Sirius hesitated, confused for a moment, then he jerked Regulus closer and spat a curse and an order to stay the fuck away from them all, especially Lupin. They had stalked away in a righteous huff leaving Regulus to lean against the table and tremble.
He could feel Remus fighting him now, fighting for control. Fortunately, Regulus had the prior knowledge of this body, and he wrenched control back with all his strength.
"Stupid, very stupid, Lupin." His voice sounded shaky, breathy, like he'd run all the way from the dungeons. "You're going to pay for that." But Lupin had receded into a seething silence again.
His legs got steadier as he made his way to the Prefect's Bath and warded the door behind him, though he doubted anyone would come near it at this time of day. He got the taps started, foregoing the bubbles, and stripped off without ceremony, then he picked up his wand again. A mirror was essential, after all, and he didn't want to stray too far from the vicinity of the bath.
Tapping the end of his wand against his chin he contemplated the tiled wall. That would do. He traced his wand over a rectangle of numerous tiles and muttered a word. Perfect.
He could sense Lupin's unease as he turned off the taps, but Regulus held his own silence as he dove into the pool and swam the length of it. Gasping, he surfaced, water streaming down his neck and back as he arched his neck back and levered himself out of the bath. His feet left wet footprints on the floor as he walked slowly to the mirror.
He faced himself full on. His dark hair looked even blacker, slicked back from his face and emphasizing his high cheekbones and his grey eyes. His skin was positively glowing, the flickering wall sconces making it glisten and casting flattering shadows along his chest and stomach. The curls at the base of his groin looked neat and oiled, setting off his pale pink cock to perfection.
"Is this what you think about, Lupin?" he asked. "At night, when my brother is in his bed and you're right across the room?"
Regulus lifted a hand to caress his throat then slowly let it drift down his chest.
"Do you stare at him through the crack in your curtains, hoping for just a glimpse of him while you touch yourself?"
Again the shame, denial...and there it was...arousal. Regulus let his hand drift lower.
"Do you think about him naked, standing before you just like this?"
Regulus wrapped his elegant fingers around his cock and pulled, once, twice, three times.
Oh, yes. Lupin could feel that.
"Do you think about him touching himself while you watch, bringing himself off for you. Just for you."
Regulus. Lupin's thought was tremulous and Regulus exulted. Don't...
"But this is what you want, isn't it? What you've always wanted?"
Regulus' cock was responding now, filling and lengthening and he focused on it, knowing Lupin had no choice but to do the same. He played up his reactions, allowing himself deeper moans, a thrust of his hips as he pumped his shaft slowly. His heart started to beat faster. Because, truthfully, it was arousing to look at himself like this knowing that Lupin was watching, too. Knowing he was looking at him and thinking of his brother. Wanting his brother.
The emotional flow between them seemed to open up as Regulus continued his display. He grazed fingernails over his nipples, hissing and arching at the sharp sensation, wetting his lips with a slow swipe of his tongue and panting in time with his fisting hand, rolling his balls in his palm and pumping his hips forward with each stroke.
Waves of lust still mixed with shame were rolling out from Lupin. It drove Regulus' arousal higher and higher. It was intoxicating.
"Watch me," he whispered, sinking to his knees and bracing one arm to the side of the mirror. He jerked his cock faster, squeezing and twisting over the head with a delicious little flick that...
...that wasn't anything like him...
His eyes were wide in the mirror, pupils blown, and the color across his cheekbones high and feverish.
Waves of want shuddered through him. Desperate, greedy, dirty...thought and emotion collided and merged and surged through them out of control.
He...Lupin...they...touched their cock. Rough strokes that pulled helpless moans from Regulus' mouth. Tighter, tighter the heat coiled, and then he...they...were swearing and shaking, eyes locked on the mirror as their climax overtook them.
"Sirius," they moaned, collapsing forward against the surface of the mirror. Slowly, they raised their hand and licked away every bit of dripping come.