Regulus noticed it. Sirius's magic, wild and churning a moment ago, smoothed out all at once and gathered toward a single point.
Not bad. He hasn't been wasting all his time messing around.
Sirius leveled his wand at the sponge on the desk.
The sponge began to change. The transformation started from the inside, the structural shift pressing outward from the core.
Shape followed. Grey-white darkened to brown, edges drew inward, four legs sprouted from the base, a tail curled upward.
A squirrel crouched on the desk, fur bristling, tail high, forepaws raised. Its black eyes flicked side to side, head tilting to study the room.
It hopped off the desk, scurried two steps across the floor, and stopped.
Sirius continued. A tap of the wand and the squirrel stretched, wings unfurling from its back, body reshaping into a bird.
A starling, pale grey feathers, circled the office once and landed back on the desk with two sharp chirps.
Another tap. The starling rounded out, ears lengthening. A rabbit.
White fur, red eyes, ears standing tall. It bounced twice across the desk.
Another tap. The rabbit flattened, limbs retracting, back arching upward. A tortoise.
Dark green shell, head poking out, inching forward at its own unhurried pace.
Sirius glanced at the tortoise and flicked his wand lazily.
A section of the desk's surface dipped inward, hollowing into a shallow pool. A match drifted from the corner of the desk, floated above the basin, and began to change.
The match head melted, the wooden shaft softened, liquefied, and trickled down into the pool, filling it to the brim.
The tortoise shifted in the water, not quite sure what to make of it.
Another flick. A fish leapt from the surface.
Not from the tortoise. He'd taken the water he'd made from the match and shaped it into a fish.
Regulus watched the sequence and gave a satisfied nod.
Not performative. He meant it. The shape-work wasn't what interested him; what mattered was the magic.
Sirius's power flowed through the transformations smooth and fluid, and the way it entered its targets differed from most young wizards.
Most people pushed from the outside in, forcing the target's form toward a predetermined shape. The longer they pushed, the harder it got, and the results lacked precision.
Sirius grew it from the inside out, let the form find its own way there. The end result might look similar, but the underlying comprehension was a different thing entirely.
It wasn't making something become what you wanted. It was knowing what it was supposed to be.
Sirius stole a glance sideways, trying to catch Regulus's expression without being obvious about it, and found him nodding, approval clear on his face.
The corner of his mouth kicked up. He yanked it back down.
He realized he was pleased. Pleased because Regulus approved.
He cursed himself internally.
He killed the thought, pulled his gaze away, and looked to McGonagall. Satisfaction there too.
Sirius stared back at the fish in the pool. Still swimming, tail sweeping side to side.
He flicked his wand upward. The fish launched from the water, hung airborne, and began to transform.
Its body swelled, limbs extending from the torso, head broadening, a mane spilling backward from the neck.
A lion landed on the desk, all four paws down, mane thick and full. One forepaw struck the surface with a low, reverberating thud.
It shook its head, yawned wide, teeth gleaming white, then paced two steps across the desk, tail lashing once.
Sirius waved his wand again. The top sheet from a stack of parchment beside the desk lifted, folding and pulling in midair, reshaping.
The edges thickened, color shifting from grey-white to brown, sprouting fur, the head elongating, antlers pushing up from the crown.
A stag landed beside the lion, a size smaller, legs long and fine, antlers branching, eyes dark and wet.
Its head tilted slightly, turning toward the lion with something that might have been curiosity.
Sirius thought for a moment, then tapped his wand once more.
The seat cushion from an empty chair in the corner floated up, tumbling through the air, transforming as it went.
The stuffing inside redistributed, the frame contracted, the fabric surface became fur.
A large dog dropped to the floor, bigger than any real dog, coat dark grey, limbs thick, ears half-drooped, tail up and wagging once.
It trotted to the lion and sniffed, then bounded over to the stag and circled it.
Three animals moved through McGonagall's office.
The lion took two steps toward the stag. The stag sidestepped. The dog darted in from the other side and bounced in front of the lion.
A paw batted it gently. It retreated, then circled the stag twice more.
The stag lowered its head and nudged the dog. The dog rolled with it, scrambled up, and kept circling.
Regulus watched the stag and the dog. His gaze lingered a beat longer than necessary.
The lion was unremarkable. Every Gryffindor loved lions.
But a stag and a large dog, together, brought something else to mind.
He looked away.
Sirius's Transfiguration had improved. The forms were beyond criticism: accurate shapes, lifelike movement.
But Regulus wasn't watching the shapes. He was watching how the magic traveled through the process. Fluid, purposeful, intent clear from start to finish.
That meant Sirius's understanding of Transfiguration had started reaching deeper.
For a third-year, this was solid work.
But he couldn't stop here. The talent was found. This was the time to push harder. Progress demanded more practice, and wasting momentum would be a shame.
Regulus thought of Lily, thought of everything he'd said to her. If Lily trained up, and one day ran into Sirius bullying someone in a corridor...
This idiot, dragged around by James Potter and their crew, wasting his days hexing Snape in hallways, throwing his time at things that didn't matter.
Yet here he was today, in McGonagall's office, working on Transfiguration with genuine effort. Proof enough that he could apply himself when something pushed him. He either needed someone keeping him in line, or a proper incentive.
So give him one.
But Regulus also knew he couldn't be the one to do it anymore. Beating him up once or twice was easy enough, but it risked triggering defiance.
On the other hand, getting beaten up by someone Regulus had trained... that ought to be educational.
Sirius was stealing glances again, that smug little smile fighting its way up, getting pushed down, fighting back up, impossible to suppress.
He wanted Regulus to see his progress. He didn't want Regulus to think he cared about his opinion.
But right now he did feel proud, and the competing impulses tangled together until his expression turned distinctly odd.
Regulus read it well enough and nodded. "Not bad. Clear improvement."
A beat. "Keep practicing."
The corner of Sirius's mouth climbed higher. He forced it back down.
He turned his head, pulled his gaze off Regulus, and looked back at his three creations.
The dog was chasing the lion's tail across the floor. The stag stood steady nearby, glanced down once, and ignored them both.
McGonagall was satisfied with Sirius, but her attention had been more on the brothers' interaction.
Letting Regulus stay and watch had carried a small worry: that he might dismiss Sirius's progress outright.
She knew where Regulus stood with Transfiguration. Spatial Transfiguration was already within his reach; he'd said as much walking in, asking to discuss it.
Which meant he'd made substantive headway.
Spatial Transfiguration fell, strictly speaking, within the domain of form transfiguration, but it was incomparably harder than transforming visible, tangible, magically accessible matter.
One of them was reshaping space. The other was reshaping objects. The gap between those wasn't a matter of difficulty. It was a difference in dimension.
Regulus could already perform spatial transfiguration. Sirius was still working conventional transformations on conventional materials.
She'd worried that a casual what's so impressive about that from Regulus could drown every drop of confidence Sirius had built over these months.
And she couldn't have said anything about it. She'd been the one who invited Regulus to stay.
Now she saw the worry had been unnecessary. The brothers got along better than anyone would guess.
Her estimation of Regulus shifted again. The child wasn't only gifted. He was decent in other ways too.
Both brothers had talent, but Regulus had already converted his into real power. Sirius was still on the road of discovering what his talent could become.
Sometimes McGonagall wondered whether certain wizards destined for greatness were simply like this.
She thought of Dumbledore.
She'd been his student and knew him reasonably well.
His power was beyond question. No one doubted it. No one dared.
But when she thought carefully, she wasn't sure what Dumbledore had been like as a student, whether he'd shown this kind of brilliance in his early years. She didn't know the specifics.
By the time she'd entered Hogwarts, he was already the Transfiguration professor. One thing she could say with certainty: Regulus was the most remarkable student she'd ever seen.
She looked at the two children before her.
Sirius, demonstration finished, had that restless energy surging back, fidgeting in his chair, wanting to say something but holding it in, rocking forward and back.
Regulus sat beside him. Still, composed. His eyes rested on the animals, studying them.
The satisfaction on his face was genuine, but McGonagall could tell it was recognition of Sirius's progress and effort, nothing more.
She pulled herself from her thoughts and turned to Regulus. "Mr. Black, your questions?"