In the fall of 1962, Regulus was a year and a half old, and Sirius Black was three.
The nursery had split into two worlds.
Sirius's side looked like a small disaster zone, toy broom parts scattered across the floor, a box of goblin-made metal puzzles spilled open like someone had tried to wage war on it.
Regulus's corner, meanwhile, stayed tidy. A few picture books sat neatly on a deep blue rug, along with a stuffed cat-raccoon doll that didn't move anymore.
It used to, until Sirius had played with it too hard and broken the charm.
That afternoon, Kreacher was cleaning the windows with magic, but his ears were angled toward the two young masters. Even his eyes kept sliding back, tracking what they were doing.
Because Sirius had just brought a miniature broom into the nursery, something he'd taken from Orion's study. It was a shrunken model of a real broom, a teaching tool used to demonstrate how flight charms worked.
"Watch this, Regulus!" Sirius shouted, loud enough to demand attention. "It's a broom. A real wizard broom. I can make it float!"
He placed it on the carpet, backed up two steps, and sucked in a deep breath. His cheeks were already turning red from the effort.
"Up!" he yelled, throwing both hands upward as if he could lift it by force alone.
The broom trembled. One end rose maybe five degrees, then dropped back down.
"Up! Up!" Sirius tried twice more. This time the broom rolled half a turn in place, but it still didn't lift.
Kreacher held his breath.
He knew the broom had been layered with a limiting charm. Only someone who truly understood the Levitation Charm, who could picture weight disappearing, could activate it.
Orion used it to test a child's instinct for magic. Sirius thought he'd stolen it, but that was exactly what Orion had wanted.
And Sirius very clearly didn't understand it yet.
"Why won't it work?" Sirius kicked the carpet, furious. "Dad can make it fly!"
That was when Regulus moved.
He pushed himself up from the rug, quicker than he usually was, walked over to the broom, and plopped down beside it.
Sirius watched him and curled his lip. "You want to try? You can't even talk."
Regulus didn't bother looking at him. He just extended his right index finger, hovering it over the broom.
Then he pointed down, lightly.
The broom rose at a slow, steady pace. When it reached eye level, it hung there in the air, perfectly still.
Sirius's mouth fell open.
The cloth Kreacher was controlling dropped straight to the floor.
Regulus pressed his finger down again, just as gently, and the broom lowered back to the carpet, settling into the exact same spot it had started from.
Sirius stammered, "You… how did you…"
He couldn't make sense of it. How could his little brother do what he couldn't?
Regulus finally turned his head. His voice was young, but clear, and he spoke his first full sentence.
"Think, then do."
"Think what?" Sirius asked automatically.
"Think it's light," Regulus said, pointing at the broom. "Don't think it's heavy."
"But it is heavy!"
"Think it isn't."
"How's that even possible?"
Regulus tilted his head, like he was searching for the right way to explain it. Then he patted the carpet beside him. "Sit."
Sirius sat down without thinking, so caught up in the moment that it didn't even register how cleanly his brother had spoken.
Regulus picked up a leaf that had drifted in through the window and placed it in his palm. "This is light."
"Yeah."
"Think it's heavy."
Sirius stared at the leaf, trying to picture it as heavy as a stone.
Nothing happened.
"Wrong," Regulus said, as if he could see right into Sirius's thoughts. "Don't think, 'It's heavy like something.' Forget it's light. Then it's heavy."
Sirius frowned.
It was too abstract.
He'd never tried to imagine things that way before.
He scratched his head, completely lost.
Regulus wobbled to his feet and went back to his corner, leaving Sirius alone to wrestle with it.
Regulus had done what he came to do.
For a three-year-old, that kind of understanding was still too early.
For him, it was different. Age had never been a limit when it came to comprehension.
After dinner, Orion summoned Kreacher to his study.
"That teaching broom," Orion asked, seated behind his desk, brow tight with suspicion. "Regulus made it levitate?"
"Yes… yes, master," Kreacher said, twisting his tea towel until his knuckles went white. "Young Master Regulus lifted it. One foot. Very steady."
"And he spoke?"
"He said a few things." Kreacher repeated what Regulus had told Sirius.
When he finished, Orion went quiet for a long time. The ancestor portraits on the study walls pretended to look elsewhere, but every one of them was listening.
"From now on," Orion said at last, "whatever Regulus wants to do, as long as it isn't dangerous, let him. Watch him, record it, and report to me every day before dinner."
"Yes, master!"
---
In December of 1963, 12 Grimmauld Place was preparing for Christmas.
Sirius Black had turned four a month earlier, and he'd entered that age where he was convinced the world existed to admire him.
He planted himself in the center of the drawing room, hands on his hips, and made an announcement to the half-decorated Christmas tree. "I'm gonna make the bells ring all by themselves!"
From the second floor, Walburga leaned over the railing. "Sirius, don't start trouble. Kreacher, hang the silver baubles higher. Last year they were too low and Andromeda nearly hit her head."
"Yes, my lady." Kreacher lifted the silver ornaments higher with a flick of his long fingers.
Regulus sat on the thick rug by the fireplace, so still he might as well have been a fern someone forgot in the corner.
The soul from another world had been in this body for three years now. He'd accepted the reality of it. This was a world of magic, and he was Regulus Black, the early-dead tragedy from the original story.
But he had no intention of reliving that tragedy.
He had bigger goals.
The stars.
The universe.
Things the original story never even brushed against.
As for Sirius?
Let him be, Regulus thought. He'd grow up to be a champion of justice, a hero who fought Voldemort.
As long as I'm alive, the Black family's resources are my stepping stone. There's no point fighting with a four-year-old.
"Regulus! Watch!" Sirius's voice yanked him back.
Sirius took a deep breath and fixed his glare on a golden bell near the top of the tree. He squeezed his face red again, both hands clawing at the air like he could grab the sound.
Magic stirred.
"Move!" Sirius shouted.
Regulus's sense for magic was unnaturally sharp, like he had an extra set of senses. He could feel Sirius's magic surging, and he could tell it was about to tip out of control.
Bang.
The entire Christmas tree began to shake violently.
The star topper fell and smacked Kreacher on the head. Candy canes clattered into each other. Glass ornaments chimed and rattled. A strand of enchanted fairy lights that could change colors on its own suddenly started flashing wildly, so fast it looked like it was glitching.
"Stop! Stop!" Walburga stormed down the stairs.
Too late.
Sirius startled at his own power. He tried to pull back, but he couldn't. Panic flooded his small face. He flailed, desperate, and the magic only became more unstable.
Boom.
Three tall windows along the east side of the drawing room exploded at once.
Glass sprayed outward, but the protective charms caught it, slowing and suspending the shards in midair. Without that, the entire street outside would've been hit.
The chandelier swung wildly. Crystal drops slammed into each other, shrieking with the impact.
"Ah!"
The portraits screamed as one. Phineas Nigellus bellowed the loudest, "Savages! The Blacks truly have fallen!"
Walburga raised her wand and hit Sirius with a strong calming spell.
He staggered back a few steps and collapsed onto the rug, staring at his hands like he'd never seen them before.
Walburga's expression was something to behold. Anger came first, sharp and immediate, but pride followed right on its heels.
"Plenty of magic," she said, her tone oddly satisfied. "Wrong direction. Next time aim it at something useless, like the ugly vases your father collects."
Sirius blinked, not understanding.
He'd expected to be yelled at.
Regulus closed his book.
This was the problem with wizard children, he thought with a quiet sigh.
Their magic rose and fell with their emotions, like a pressure cooker without a safety valve, always one wrong moment away from blowing.
Kreacher began cleaning up the mess. Walburga gave Sirius a complicated look, then turned and went back upstairs.
Sirius sat on the carpet, staring at his hands, then at the shattered windows, then finally at Regulus.
"I did it," he whispered.
Regulus nodded. "You did."