Regulus raised an eyebrow, mildly surprised.
His first instinct was that Sirius had done something wrong, gotten caught, and was in the middle of being dressed down.
He looked him over, scanning for the telltale signs: tension in the shoulders, defensive posture, the deflated look of someone who'd just had their ear chewed off.
The way he sat. His expression. Where his hands were.
But Sirius wasn't here for a scolding. He'd actually been coming to McGonagall's office regularly.
Ever since that Transfiguration lesson where the professor had kept him after class, told him he had an instinct for form, and given him that copy of Advanced Transfiguration, he'd gone back and read it properly.
The deeper he went, the more it hooked him. Whatever he couldn't make sense of, he'd bring to McGonagall. She'd explain it, he'd go away and practice, and when he cracked it, he'd come back with more questions. It had become a rhythm.
James knew. Lupin knew. They both said he'd changed lately, that he was quieter.
Sirius couldn't explain it himself. He'd opened the book and something had grabbed hold, a curiosity he couldn't push down. He wanted to practice, wanted to understand, so he did.
Before, it had been show up for class, leave when it ended. Now he was seeking McGonagall out on his own, and the questions he asked ran deeper than anything he'd bothered with before.
Transfiguration itself hadn't gotten harder. He'd simply started walking further into it.
The shift was night and day from his old classroom self, that bored expression, the couldn't-care-less slouch.
Even he could feel the difference.
When Regulus walked in, something flickered across Sirius's face. His body stiffened, just slightly.
He stared at that face and an absurd feeling leapt through him.
Like someone who'd been secretly putting in the work, suddenly caught by the one person he least wanted to know about it.
He knew the gap between himself and Regulus was laughable, but after McGonagall's recognition, that competitive streak had surfaced on its own.
Not to match Regulus. He just couldn't stand falling too far behind.
So he'd been putting in the hours quietly, practicing Transfiguration harder than anyone, telling no one.
And now, mid-practice, Regulus had walked right in on it.
A tangle of feelings rose through him: guilt, panic, the raw embarrassment of being seen through.
He straightened in his chair, pulled his hands off the desk and set them on his knees. His eyes darted sideways, then snapped back.
He stared at the parchment on the desk, pretending to read it, absorbing nothing.
His expression hovered somewhere between casual indifference and not-quite-managing casual indifference, stuck halfway, slightly absurd.
Regulus looked at him and thought he'd found the tell.
The shifting eyes, the fidgeting, the restless energy radiating off him in waves.
Caught red-handed. Definitely in trouble. And now I've walked in and he's squirming.
Regulus glanced at McGonagall. She sat behind her desk, quill still in hand, parchment half-covered in annotations.
Sirius had been a handful at Grimmauld Place. Apparently Hogwarts hadn't improved matters.
As family, he felt he ought to say something.
He stepped forward and gave McGonagall a polite nod. "Professor, forgive the interruption. I had a few questions about Spatial Transfiguration. If this isn't a good time, I'm happy to come back."
Then he turned to Sirius, expression gentle, carrying the patient tolerance of an older relative addressing a younger one, touched with a note of apology. "Sorry about this, Professor. I hope Sirius hasn't been too much trouble."
McGonagall looked up. Her gaze settled on Regulus, and something odd crossed her face.
Her eyes lingered on him for a moment, slid toward Sirius, came back. One corner of her mouth twitched upward, then pulled back, a laugh caught and contained.
She said nothing. Did nothing. But something flashed behind her eyes, there and gone, and she adjusted her spectacles, cleared her throat, and let the silence hold.
Sirius shot upright in his chair, face flooding red.
Anger and mortification in equal parts, the suffocating indignation of what in the hell are you saying.
His mouth opened, closed, but Regulus's perfectly earnest expression left him with no idea where to start.
He glared at Regulus, then at McGonagall. Her barely suppressed amusement only made it worse.
He sucked in a breath, tried to shove the anger down, failed. Drew another breath. Still failed.
Regulus watched the reaction and thought, Temper's the same as ever.
McGonagall gave a light cough.
The ordinarily stern Head of Gryffindor now had unmistakable laughter in her eyes.
"Mr. Black," she said, glancing at Sirius, then back to Regulus, "Sirius is not in trouble."
A beat. She seemed to decide the statement lacked sufficient rigor.
A sharp look at Sirius. "Not this time, at least."
Sirius was still standing, eyes wide, staring straight at Regulus with an expression that screamed did you hear that.
Regulus gave Sirius a mildly surprised look, then turned back and inclined his head to McGonagall. "Thank you, Professor. I appreciate you looking after him."
Laughter flickered in McGonagall's eyes again.
In all her years teaching at Hogwarts, she'd encountered every variety of student imaginable, but these two Blacks were something else entirely.
The world said the brothers were estranged. One Sorted into Gryffindor, the other into Slytherin, the family fractured along ideological lines.
Sirius was the Black family's traitor, severed from them, a stranger to his brother, the two of them on opposite sides of everything.
That was the story, and it wasn't merely rumor. At school the brothers barely interacted at all.
But this scene didn't match any of it.
The younger Mr. Black's first instinct upon entering had been to apologize to a professor on his brother's behalf.
Tone warm, manner impeccable, every gesture beyond reproach. Like a parent at a school meeting.
McGonagall found herself wondering, What on earth is this child? How does the Black family produce someone like this?
Sirius stood beside him, watching Regulus and McGonagall exchange pleasantries, feeling like he was being publicly executed.
His face burned. The tips of his ears were on fire. Something lodged in his throat, too solid to swallow, too stubborn to cough up.
Regulus turned his head and looked at him, expression mild, voice patient. "Sit down. Don't be rude in Professor McGonagall's office."
Sirius's eyes went round. He swept a quick glance across the desk.
If he Transfigured the quill into a maggot and shoved it into Regulus's mouth, how many steps would that take, could he finish before the professor reacted...
Then he noticed McGonagall watching him over the rims of her spectacles.
He dropped back into his chair. The legs scraped against the stone floor with a dull thud.
McGonagall ignored him and addressed Regulus. "Please, sit, Mr. Black. As it happens, your timing is good. I was about to review Sirius's Transfiguration work. Perhaps you'd like to observe?"
Regulus glanced at Sirius once more, then turned back and nodded. "Thank you, Professor."
He sat down beside Sirius. The two chairs were close together, the brothers side by side facing McGonagall. One sat straight-backed and composed. The other looked ready to launch out of his seat at any second.
McGonagall swept a glance over the pair and drew a quiet comparison.
Sirius's magic churned, volatile, like water at a rolling boil, bubbling up and over, impossible to contain.
Emotion and magic had always been the same thing in him. Happiness made his power surge; anger made it spike.
Regulus's magic ran calm, steady, a river flowing without a ripple on its surface.
The same surname. The same bloodline. Nearly opposite in every quality that mattered. That was uncommon.
Emotional stability wasn't always a virtue. Sometimes it meant distance, meant learning too young to hide yourself away.
But in magic, the control and endurance that stability afforded were undeniable advantages.
Plenty of gifted witches and wizards spent their entire lives wrestling their own emotions. Win, and they could wield their power. Lose, and half their ability was wasted.
Someone like Sirius, whose emotions and magic were bound together, could be devastating at peak intensity.
But the swings were wide. He needed time, needed to learn how to channel that raw force into something he could call on at will, rather than letting it come and go with his moods.
Neither approach was better. Only better suited.
She'd watched Sirius's progress with satisfaction. His instinct for form was genuine talent.
If only he'd behave himself a bit more.
The after-hours pranks, the corridor confrontations, she was well aware of all of it. But she kept that thought to herself. That was a separate matter.
Then her mind turned to Regulus.
This child's understanding of Transfiguration had already outstripped anything the classroom could offer.
Some of the questions he brought her required real thought before she could answer. She wasn't even certain, truthfully, how far he'd gone.
But she knew that what Regulus showed her was only what he chose to show.
Anyone who could tame Fiendfyre to that degree didn't keep only clean, presentable magic in his arsenal.
The things he didn't mention, the things you couldn't bring to a professor's office, those were where his real capabilities lay.
That wasn't a bad thing. Every wizard who walked deep enough had things they didn't put on display.
Regardless, both brothers were gifted, and both had personality to spare.
Sirius was easy to read. Reckless, impulsive, acted before thinking, offended people without realizing it.
But he wasn't bad at heart. Injustice angered him. Cruelty toward the weak enraged him. He just couldn't always tell where the line fell between standing up for what was right and picking a fight.
His sense of justice was real. Only his way of expressing it needed work.
And Regulus?
McGonagall turned the question over and couldn't find the right word.
What this child did, at the very least, had nothing to do with justice.
But Dumbledore said he had a Patronus, the magical creature variant, capable of traversing space.
Dumbledore said there was light in him. She trusted Dumbledore's judgment.
McGonagall set the thought aside, pulled herself back, and looked at Sirius. She raised a hand.
"Begin, Mr. Black."
Sirius was still glaring at Regulus, something coiled tight in his chest, not quite anger, not quite anything he could name.
That act Regulus had pulled, the gracious younger brother apologizing on his behalf, had made his skin crawl. As though he were the one in trouble and Regulus had swooped in to smooth things over.
But he didn't want to look bad in front of Regulus.
These past months hadn't been wasted. His Transfiguration had improved. McGonagall herself had said so.
He'd show him.
He wouldn't admit he cared what Regulus thought. But he wanted Regulus to see.
The feeling made no sense to him, a knot of stubbornness and pride, uncomfortable but impossible to ignore.
He remembered what Regulus had said over the holidays.
He'd found his talent. Transfiguration. He was good at it, truly good.
He wasn't the Sirius who'd been knocked flat by one punch at Grimmauld Place anymore.
He drew a deep breath and pulled out his wand.