Chapter Text
The worst day of Regulus Black’s life had been the day his cat, Kreacher, died. Or at least, that’s what he thought—until his brother announced he was leaving London for some inheritance arrangements and, worse, that James bloody Potter would be moving in to look after him.
After their parents had died in a car crash—Regulus just ten, Sirius barely thirteen—their lives had shifted into something almost manageable. A housekeeper looked after them until Sirius turned eighteen, and after that, Sirius took the reins, making sure Regulus ate, got to school, and didn’t disappear into the dark corners of their enormous house. Regulus went to a normal high school, Sirius to a boarding school, where he found James Potter and immediately decided he had met his soulmate.
The last time Regulus had seen Potter, he had been thirteen—awkward, quiet, still smaller than his brother’s best friend. He remembered James vaguely as the loud one at Sirius’s birthday party, the one who spilled Coke on the carpet and laughed about it instead of apologizing.
But Sirius never shut up about him. After his first term at boarding school, James was all Sirius talked about. The way he talked, the way he cracked jokes, how he made life bearable in a place Sirius otherwise hated. Regulus, who had always been close to his brother, found himself sidelined by this new friendship, and something hot and bitter took root in him. From that day forward, he decided he hated James Potter.
So when Sirius, suitcase in hand, told him he’d be gone for a month and James Potter would be moving in, Regulus nearly lost his mind.
⸻
“Sirius, I’m seventeen. For fuck’s sake. I don’t need a babysitter.”
Regulus stood stiffly in the doorway of his bedroom, arms folded tight across his chest. His brother looked at him with maddening patience, the way only Sirius could.
“Reggie, I know,” Sirius sighed, scrubbing a hand through his hair. “But I just… I need some assurance, alright? That you’ll be okay. Nothing happens while I’m gone. It’s only for a month, and James isn’t that bad.”
Regulus narrowed his eyes. “Not that bad? He’s insufferable. Don’t you trust me enough to take care of myself?” His voice sharpened. “I’ve been living like this for years while you were off at school. And of all people, you chose James bloody Potter?”
The air between them grew hot, tension sparking like static. Sirius’s jaw tightened.
“First of all, you had a maid looking after you back then, so don’t rewrite history. And second—James is a great person, and I won’t stand here while you slag him off. He’s staying, and that’s final.” Sirius slammed the door on his way out, leaving Regulus seething in the silence of his room.
⸻
The next morning, Regulus ate his breakfast in sullen silence while Sirius hoisted his suitcase by the door.
“Come on, Reggie.” Sirius’s voice softened. “I know you don’t like James much, but I promise you it won’t be bad. You won’t even notice he’s here. Maybe you’ll even get along.”
“Maybe I’ll grow wings too,” Regulus muttered, stabbing his toast.
Sirius ignored him. “I know you’re seventeen and capable, but I need to know you’re alright. Humor me.”
Regulus rolled his eyes. “You could’ve asked literally anyone else. Even the maid. She’d have been better than him.”
Sirius chuckled, shaking his head. “You’re not a kid anymore, Reggie. You don’t need a maid. You just need someone around. James will be busy with his company half the time, anyway. You’ll barely see him.”
Of course Potter had a company. CEO at twenty-one, or whatever ridiculous age he was. Regulus pitied his employees; he’d rather drown than work under James Potter.
Still, when Sirius dropped his suitcase and pulled him into a hug, Regulus gave in. They didn’t hug often anymore, but when they did, it made him feel safer, grounded. A little part of him knew he’d miss Sirius while he was gone—but he’d never admit it.
“Sirius, let go,” he muttered into his shoulder. “It’s not like you’re leaving for war.”
“Could’ve fooled me,” Sirius teased, releasing him. “I’ll miss you, cold-hearted bitch that you are. Don’t forget—James will be here when you get back from school. Try not to scare him away, alright?”
Regulus scowled, but his brother only laughed, ruffled his curls, and disappeared out the door.
Regulus had already decided: he would make James Potter’s life a living hell.
⸻
School did nothing to improve his mood. At his locker, his friends—Barty, Evan, Dorcas, and Pandora—were waiting.
“Oi,” Barty called, grinning. “Who pissed in your cornflakes this morning?”
“James fucking Potter,” Regulus snapped.
The group dissolved into laughter, the kind that made his ears burn.
“What’s he done now?” Pandora asked, her smile soft but teasing. “Isn’t he leaving with your brother? He’s practically glued to Sirius’s hip.”
“Apparently not. Sirius dumped it on me yesterday—Potter’s moving in. Looking after me like I’m some kind of pet.”
Evan wheezed, clutching his side. “Oh, this is brilliant. Tell me you’re planning something.”
Regulus’s lips curled into a sharp smile. “Don’t worry. By the time I’m finished with him, Potter will wish he was never born.”
⸻
James, for his part, hadn’t thought twice about saying yes when Sirius asked him. Babysitting a teenager for a month? Easy. He barely remembered Regulus—quiet kid, bookish, always lurking at the edges of parties. James had pictured the same thing now: a skinny schoolboy hiding in his room.
Which is why, when the front door creaked open that afternoon, James nearly dropped the spatula.
Holy shit.
Regulus wasn’t a boy anymore. He stood in the doorway, curls falling over his shoulders, a crop top clinging to his narrow frame, low-slung jeans revealing pale skin at his waist. Piercings caught the light—earrings, a nose stud, even a glint of silver at his stomach.
James’s brain short-circuited.
“Uh—hey, Reggie,” he stammered, hating himself instantly. “I thought—you’d be hungry. I made some food, if you want.”
Regulus’s glare could have frozen fire. “First of all, don’t call me Reggie. That’s not my name, and we’re not friends. Second, I’m not hungry.” He swept past, heading upstairs without a backward glance.
James stared after him, dumbfounded. So much for this being easy.
⸻
Regulus, meanwhile, was fuming. Potter looked unfairly good—grey joggers, white compression shirt, glasses slipping down his nose as he stirred something on the stove. Who the hell gave him permission to look like that?
By nine, Regulus couldn’t take it anymore. He fired off a message to his group chat.
Regulus: I want to get fucking drunk.
Barty: fuck yeah
Evan: thought you’d never ask ;)
Dorcas: wohooo
Pandora: usual spot?
Jacket on, phone in hand, he slipped downstairs. James was at the kitchen table, glasses on, typing furiously on his laptop. He looked up just as Regulus reached for the door.
“And where do you think you’re going, if I may ask?”
Regulus rolled his eyes. “No, you may not ask.”He reaches towards the door again.
James stood up and his hand shot out, catching his wrist. His grip was firm, steady. “Not happening. It’s late. I’m not letting you run off and do something stupid.”
“Let me go.” Regulus yanked free, fury blazing in his eyes. “You’re not my father. You’re not my brother. You’re no one. Don’t pretend you get to decide what I do.”
He shoved James hard, watched him stumble, then bolted outside, slamming the front door behind him.
⸻
Three in the morning. James was still on the couch, half-asleep, waiting. When the front door opened, Regulus staggered in, drunk and sharp with defiance.
James rose instantly. “Where the hell have you been? You reek of alcohol.”
Regulus swayed, glaring. “None of your business.”
“The hell it isn’t,” James snapped. “You disappear for hours, come back wasted, and expect me to ignore it? Not happening.”
“Yes, that’s exactly what I want you to do.”
“No.” James’s voice was steel. “While I’m here, you don’t pull reckless shit like this. You tell me where you’re going. Even if I have to put a fucking tracker on you.”
Regulus barked out a laugh, furious and wild. “Tracker? Who the fuck do you think you are? You don’t get to control me. You don’t get to pretend you care. Stay out of my life, Potter.”
He shoved past him, storming upstairs, the slam of his bedroom door shaking the walls.
James sat down heavily on the couch, scrubbing his hands over his face.
Well. What a first day.