Chapter Text
Regulus did not have time for this.
He had prefect duty. And quidditch practice. He had a paper he was writing for the Westphalian Society of Brewmasters Journal. He had a scene to plan with Barty before he lost his temper and cursed a hall full of Hufflepuffs again (no one required maintenance spankings like Bartemius Crouch Jr.).
No Regulus had no time to spare, and certainly not for whatever fresh nonsense his brother had cooked up.
But that had not stopped Slughorn from summoning him to his office with an ominous note announcing that there was “ an issue with your brother that requires your immediate attention. ”
So here he was, derailing his day for god knows how long to deal with Sirius plus at least an additional half hour of the sycophantic bullshit he’d have to feed Slughorn to in order to keep the man happy.
Sighing, Regulus raised his hands and knocked.
He was surprised to hear the muffled sound of a crash coming from within the room.
“Not now! I’m afraid I’m rather– preoccupied at the moment!” Slughorn’s voice was more harried than Regulus had ever heard it.
“Umm... sorry to bother you professor… It’s Regulus Black, I believe you sent for me?”
Why on earth were they having this conversation through a door?
“Oh! Mr. Black! Thank goodness you’re here at last!”
More banging, and a yelp accompanied by a high-pitched cry of “hands where I can see them, fat man!” and Regulus’ curiosity finally got the best of him.
He opened the door to find…
Well, chaos was kind of Sirius’ brand, but he’d really out done himself this time.
The door between the office and the classroom beyond was ajar - where the half dozen abandoned cauldrons, scales, and potions sets made it clear that the class had evacuated in a hurry. Some kind of emergency barrier must have triggered, because despite the open door, James Potter and Remus Lupin were hovering just inside the classroom, clearly unable to cross the threshold.
Slughorn had somehow managed to cram his considerable mass under his desk, where he was (barely) maintaining a shield charm as various potions ingredients flew off the shelves, bounced off the shield, and then crashed to the floor.
Standing on top of the desk, black curls flying, silver eyes flashing, and face screwed up in rage - was Sirius.
He couldn’t have been more than ten years old.
The words were out of Regulus’ mouth before he even realized what he was saying. The was just something so natural about channeling his inner Walburga when Sirius was like this
“We do not stand on furniture, Sirius Orion!”
Sirius froze.
The objects - which Regulus now realized had been moving through without a spell (propelled instead through Sirius’ own personal brand of accidental magic and sheer force of will) - also froze, and then promptly smashed to the floor.
The barrier between the classroom and the office dissolved in a blink (Good Godric, had that been Siri too?) leaving Potter and Lupin sprawling on the floor. But for once, Sirius didn’t have eyes for them.
No, for the first time in six years, his brother’s attention was focused solely, and completely, on Regulus.
“Reggie?”
—---------
“I won’t!” Sirius proclaimed, half an hour later in the Headmaster’s office. Regulus still did not have time for this - although it was becoming more and more apparent that his brother’s deaging would inevitably become his problem.
“Mr. Black, I assure you, Mr. and Mrs. Potter are the kindest of wixen—” The Headmaster began, but Sirius cut him off again.
“I’ve never met them! No! You cannot make me! Reggie - on doit appeler maman, ils veulent m’enlever! ”
“Mr. Black, I thought we’d agreed to keep the conversation in English–”
“ Maman m’a dit qu’il aimait les petits garçons, mais je n’aurais pas pensé qu’il serait aussi ouvert… ”
“I do, of course, speak French, you know, Sirius…”
“ Bien sûr, vous voulez les garçons français aussi… ”
“Mr. Black, that is quite enough!” McGonagall cut in - and, huh, Regulus wouldn’t have pegged her as a francophile. If he didn’t have such a headache, he’d be at least partially grateful to Sirius for the useful intel.
“I don’t know you, either!” Sirius said turning to her, his small face screwed up in defiant fury. But then his eyes flew to Regulus’ and for a second, his guard dropped.
And gods damn it.
He was scared. Regulus knew that look - had seen it on his brother’s face dozens of times when he went toe to toe with Walbruga. Sirius was scared, and was not backing down, and even though Regulus really really did not have time for this he couldn’t leave Sirius to fend for himself all on his own.
“Headmaster,” he began, and by the slight quirk in Dumbledore’s lips as he looked at Regulus he could tell this had been the plan all along. Fucking manipulative wanker.
“Yes Mr. Black?”
Smug arsehole.
“As I’m sure you are aware, I turned seventeen a few weeks ago.”
“Why yes. My felicitations on your recent elevation to adulthood.”
“Quite. In any event, I’m sure that… if over the next few days Sirius needs tending...”
“Wait that’s an option? I want to go with Reg!” Sirius said, leaping up and almost tripping over his (still too long) robes. It was ridiculous no one had righted them yet.
“Stay still, Sirius Orion.”
“Oh…umm. Ok,” Sirius said, only squirming a little bit as Regulus shrunk his robes. Why was he blushing? Nevermind, Regulus would figure it out later.
“I’m afraid,” Dumbledore cut in, “that it may be more than a few mere days. Professor Slughorn and Madam Pomfrey had a chance to look at the potion that Mr. Snape was working on before he inadvertently tripped and spilled it onto Mr. Black…”
Absolute complete bullshit. If his parents were there, they’d have gotten Snape expelled already.
“And unfortunately well… the only safe way to age Sirius back to his proper age without any lingering signs of immaturity…”
Did that mean physical or mental?
“Is to go, well. About one year a week. To keep on the safe side.”
“Eight weeks?”
“I’m afraid so, yes.”
“Well, I’m sure two weeks from now at the latest he’ll be begging for you to bring the Potters in, and then they can take over.”
“Ah, well. The thing is, we won’t be restoring his memories until he’s back to his proper age. They don’t parse well, memories, they tend to group thematically rather than chronologically, and well, if we try to restore them piecemeal we could end up destroying them.”
“So every week, when Sirius ages…”
“He’ll see an increase in his power, and physical development of course, potentially even some muscle memory of spells - you’ll have to let me know, his is something of a unique case. But as far as his memories, he’ll have the memories he has now, and… well memories of whatever you’ve done in the preceding weeks I suppose, but nothing else.”
How many times had he wondered what Sirius would be like if he hadn’t met James Potter on that godsforsaken train?
Part of him thought the Headmaster was lying about the best way to age his brother up. Something in the twinkle of the manipulative old man’s eye told him that Dumbledore knew he was dangling a temptation that Regulus could never refuse.
He hated being played.
But the old man had won this round.
“Alright. But he stays with me.”