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Sirius threw the ball as far as he could, laughing as Regulus ran after it as quickly as his short legs could carry him. He didn’t notice the rock in his way until it was too late. He went tumbling to the ground. Instead of picking himself up or even exclaiming in pain, he just laid there with his stomach pressed into the cool autumn dirt.
“Regulus?” Sirius approached him cautiously. Nothing about tripping over a rock could be any worse than the punishments they were subjected to on a daily basis, but Regulus was never this quiet when he got small cuts or scrapes.
As he got closer, Sirius noticed that Regulus was staring at the ground right in front of him. Sirius followed his gaze and could just barely make out a small tooth lying in the grass. He sighed. That was no surprise. Regulus had been fiddling with the tooth nonstop for days, earning slaps from their parents each time his fingers went in his mouth. It was only a matter of time before it finally came free.
Without speaking, Regulus plucked the tooth from the grass and jumped up. He flew towards the house. Sirius watched him go for a second before his mind could catch up with what was happening. He took off running after Regulus as he flew through the door and straight up the stairs.
“Regulus?” Regulus didn’t pay him any attention as he kept hurrying up flight after flight, his breathing growing heavy. “Where are you going?”
The younger brother didn’t stop until he’d made it to his bedroom. Sirius narrowly avoided getting hit in the face with the door when Regulus threw it open. Still slightly dazed from the near miss, he only got a glimpse of Regulus shoving his tooth under his pillow.
“What are you doing?” Sirius asked, his face scrunching up.
Regulus patted the pillow down flat. “Leaving it for the Tooth Fairy like Andromeda told me about,” he said, puffing out his chest as if shoving a tooth under his pillow was something to be proud of.
Sirius’ stomach sank. He’d never heard of this Tooth Fairy, but if Regulus was parroting weird things Andromeda had told him, they were undoubtedly dangerous. Sirius would admit to himself that he was just as fascinated as Regulus by the stories she passed on from her boyfriend, but at least Sirius knew not to repeat them.
“What did she say about the Tooth Fairy?” he asked in a whisper.
“She’s a fairy who visits kids after they lose a tooth. You put your tooth under your pillow, and she takes the tooth and leaves money instead. It’s a thing the Muggles do.”
Sirius’ throat stung. He looked behind them for possible signs of their parents, but all he could hear was Kreacher trundling about. Kreacher at least wasn’t a threat to Regulus. Their parents were a different story. They usually had better things to do than watch their children, but Sirius could never be too sure. They had a nasty habit of showing up at the worst times.
Without bothering to explain himself, Sirius crossed the room and threw aside the pillow, snatching Regulus’ tooth up himself.
“What are you doing?” Regulus shouted, tugging at Sirius’ arm in a fruitless attempt to get it back. “It’s my tooth.”
“Regulus, stop! Listen to me. That Tooth Fairy story is extraordinary, but it’s only a Muggle fantasy. She doesn’t exist.”
“You don’t know that,” Regulus said petulantly, stomping his foot for emphasis. “We can try and see what happens!”
“How do you think Mother and Father will react if they find out you're trying Muggle stuff?” Sirius shot back, crossing his arms against his chest. He enjoyed the height advantage he had over his brother in moments like these.
Regulus looked guilty for the first time, but he wasn’t ready to give in. “She’s a fairy! That means she’s magical. The Muggles just happen to know she exists.”
Sirius sighed. Maybe there really was a fairy out there who’d made it her life’s mission to give gifts to Muggle children, but it was still too risky if their parents found out. They weren’t much more fond of fairies than they were Muggles.
“How much money does she give you?” he asked instead.
Regulus’ brow furrowed. “I don’t know,” he admitted.
“I’ll give you all my allowance if you don’t put this under your pillow.”
Regulus’ bottom lip jutted out. “That’s not the same.”
Sirius growled in frustration, and in a burst of uncontrolled magic, the tooth shattered in his hand. He opened his palm flat, staring at the tiny shards of enamel. Regulus cried out, tears beginning to flow down his face.
“Why’d you do that!?” he shouted. “I just wanted to see the—”
Sirius surged forward, dropping his hand without care for where the shards of tooth fell. He covered Regulus’ mouth and glanced towards the door. Still no signs of them. They were using silencing charms no doubt.
“Stay quiet,” he snapped, much sharper than he usually used for Regulus. “Don’t say a word to Mother or Father. Got it?”
Regulus nodded even as tears continued to roll down his face. Sirius made a sharp turn and stalked out of the room, not able to stomach turning back.