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Okay, this situation was not Sirius’s fault.
See, it all started when he caught word of his brother getting involved with certain…unsavory people. Which is to say, he looked at the Marauders’ Map and saw the dots labeled Regulus Black and Severus Snape next to each other in the library. He’d been willing to write this off as a bizarre, one-time, occurrence. But then it happened again. And again. And again.
Which meant that his little brother was knowingly associating with Snape.
He’d known he had to rectify that at once.
He recruited James first, of course, as an invisibility cloak was crucial on this sort of endeavor. Remus came next; Sirius cornered him when he was engrossed in a book (the best time to accost him, as he would agree to near-anything in order to be left alone), and after a fair bit of pleading, he conceded with a weary sigh. Peter kindly declined his invitation with an “Oh, fuck no, I’m not getting involved in that mess,” which left the rest of them to cram themselves beneath the cloak and set off on their mission.
Possibly this had been ill-planned, seeing as they were no longer the size they were at eleven years old. Remus, who’d shot up like a beanstalk, was forced to awkwardly crouch over with his back hunched. Sirius and James weren’t that much better off. Regardless, they made do.
“James, would you stop fidgeting?”
“I’m sorry, I really need to pee!”
“Bloody hell, I don’t see him anymore. Where’d he go?”
The cloak jostled with movement when James shrugged. “Shall I check the map?”
“No, I’m sure he’s just around the corner, probably talking to Snivellus again, c’mon—”
“Ow, Pads, you stomped on my foot.”
“Well, I’m sorry you’ve got such massive toes—“
“I have not, you tosser—“
“Please shut up,” Remus said.
“Shutting up.”
“Sorry, Moony.”
They quieted for a moment, and Sirius craned his neck around the corner of the hallway to catch a glimpse of where Regulus disappeared off to.
“Hear anything interesting?” came a voice behind him.
“No, because I can’t bloody find—“
“Wait, who said that?” James asked.
“Wasn’t it you, Moony?”
“No.”
“Oh,” Sirius said. “Shit.”
“Bollocks,” Remus added.
Sirius ducked out from underneath the cloak, turning around to face his very unimpressed-looking brother. “Hi, Reggie.”
“Don’t call me that,” Regulus said, arms crossed. “What the hell do you think you’re doing?”
“Um.” Sirius turned to look beseechingly at James. “Jamie, what was it we were doing?”
James, still half under the cloak, looked at him like a deer in headlights. Too late, Sirius remembered how truly terrible he was at lying. “Uh,” he said. “Mischief! We were doing some mischief here in these halls, putting firecrackers in the toilets, really, I wouldn’t recommend using the restroom for the next—“
“Oh, for Merlin’s sake,” Remus groaned. “We were spying on you.”
“Moony!” Sirius said, scandalized and betrayed.
“And what, pray tell, possessed you to do that?” Regulus asked.
“I was—“
“He thinks you have the Dark Mark,” Remus interrupted.
Sirius whipped his head around to glare at him. “We are going to have words about this later,” he said furiously.
Remus shrugged, unconcerned. “I’m out, I‘ve got a Charms essay to finish. Have fun, you lot.”
Sirius longingly watched him trot off before turning back to Regulus. “How did you even know we were there?” Sirius asked suspiciously. “Dark magic, perhaps—“
“Your feet were sticking out from under the cloak, idiot,” Regulus told him.
Ah. That would do it.
James cleared his throat behind him, folding the invisibility cloak up and stuffing it into his pocket. “Well, I think I should leave you two—“
“Don’t you dare,” Sirius warned.
James sighed and moved to stand next to him. “Alright.”
“Show me your arm,” Sirius demanded.
Regulus looked at him coldly. “No.”
Sirius reared back. “No?”
“I have nothing to prove to you,” Regulus said. “Or have you already forgotten that you’ve been disowned?”
Next to him, James grimaced.
“Of course I haven’t forgotten,” Sirius snapped. “Tell me, how long did dear Walburga wait before searing my name from the family tree?”
Regulus tilted his head. “A day. She was convinced you’d come back with your tail between your legs.”
“Ha,” Sirius said. “Fat chance.” Then he shook his head to refocus. “Your distraction tactics won’t work,” he told Regulus.
“What distraction tactics?”
“Your arm,” Sirius grounded out. “Show it to me.”
Regulus rolled his eyes. “Salazar’s sake, here.” He pulled back the sleeve of his robes to show his left forearm, and Sirius braced himself to see swirling black lines.
He blinked. Blinked again to make sure he wasn’t hallucinating.
Regulus’s skin was devoid of any marks.
Sirius didn’t even realize how tense he’d been until he relaxed. “I’m not too late,” he said, relieved beyond measure. James patted him on the shoulder for comfort. “Why have you been hanging around Snivellus, then?”
“Severus,” Regulus said pointedly, “happens to be exceptional at Potions.”
“He’s tutoring you?”
Regulus scowled. “Don’t be ridiculous. I also happen to be exceptional at Potions—we’ve had some intellectually stimulating conversations on the subject.”
“Intellectually stimulating,” Sirius repeated with visible disbelief.
“If I’m understanding this correctly, you thought that just because I was ‘hanging around’ Snape, I had joined the Dark Lord?”
“Well, it wasn’t just that,” Sirius said. “Our parents aren’t helping matters. And, y’know, neither is the fact that you call him the Dark Lord.”
Regulus tuts. “Force of habit. Where is this going?”
“Just—don’t associate with Snape,” Sirius requested.
“Oh, I’m sorry, would you rather I discuss the merits of crushing a Sopophorous Bean with Mulciber?”
Sirius groaned in anguish and dropped his forehead onto James’s shoulder. “Prongs, help me out here?”
“I think what Sirius means—“ James started.
“I don’t need to listen to my replacement, thank you,” Regulus snapped.
“Replacement?” Sirius and James asked in unison.
“Yes, that’s right,” Regulus said, glaring at James. “Brother-stealer.”
James looked to be speechless. “I didn’t steal him—Padfoot, did I steal you?”
Sirius considered the possibility. “Maybe a little bit? I let myself be stolen, though.”
“Are we done here?” Regulus asked. “Because I do have things to do—“
“Wait!” Sirius protested, a hazy sort of desperation taking over him. “Reggie—“
“Don’t call me that.”
“Is—are you alright? Is Mother…”
“Is Mother what?”
“Is she hurting you?” Sirius asked softly. “Because if she is, or even if she’s not, you could leave, you could join me—“
“What, and live with him?” Regulus asked, gesturing at James. “No thanks.”
“Or we could get our own place, we could figure it out—“
“Sirius,” Regulus said, more gentle than he’d expected. “I can’t.”
“Why not?”
“You know why.”
“No, I really don’t,” Sirius insisted. “What is it, the family needs you? You’re the heir now, so you have to stay? Reggie, you don’t have to do anythi—“
“Muffliato,” Regulus whispered, and the air took on a sort of hazy quality.
Sirius looked at him, confused.
“Look, I’m only going to say this once, so you better listen, got it?” Regulus stared at Sirius until he nodded. “I made my choice. You made yours. We’re on opposite sides, for better or worse, Sirius. Accept it.”
Sirius felt himself go cold. “Fine,” he forced out, hardly recognizing his voice, hating it all the same. James’s hand on his shoulder suddenly felt more like a weight dragging him down than an anchor keeping him shored, so he shook it off. “Of course. Talking to me must be below you, Regulus.”
“Well, don’t call me that, either,” Regulus said, wrinkling his nose in disgust. “Sounds weird coming from you.”
Sirius ignored him. “Let’s go, James,” he said. “Got things to do, places to be.”
“Wait,” Regulus interrupted.
Sirius refused to let the little glimmer of hope in his chest grow.
“Don’t hate me,” Regulus said. He lifted his hand like he wanted to touch Sirius and then lowered it back to his side like he’d thought better of it. “Just. I know that’s a lot to ask. But please don’t hate me.”
“Thought you didn’t care what I thought of you,” Sirius said icily.
Regulus sighed. “I know what I said.”
Sirius pursed his lips. “I don’t hate you,” he offered. “I don’t—I don’t think I can.”
Regulus nodded in response, just once, sharp. “Good, that’s good. I don’t think I hate you, either.”
“Look at you two, communicating,” James said fondly.
“Shut up,” Regulus and Sirius told him.
“Shutting up.”
“I also have an essay to write,” Regulus said. “Transfiguration.”
“Right,” Sirius replied. “I should go check on Remus.”
“Right,” Regulus repeated. “See you, then.”
“See ya, Reggie.”
Regulus shot him a scathing look before walking away, but didn’t correct him. Sirius took it as progress.
“Big steps taken today,” James noted.
Sirius hummed. “C’mon,” he said. “Moony and Wormtail must be bored to death without us.”
“Oh yes, we do light up their lives, don’t we?”
Sirius laughed. “That we do, Prongs. That we do.”