A/N: Er, so I totally meant to write something cute, about Regulus' animagus form being a cat or something, and then my brain thought this would be fun instead… idk why.

Using two of my prompts from the Quidditch Supplies Mystery Box #3:

(creature) Cat

(song) On the Inside – Daughtry

Word count: 1064

Regulus tried to breath, but he kept forgetting how.

There was something he'd done – he'd drunk a potion, hadn't he? He hadn't known what it would do, but he'd known there was no way around drinking it. He'd made Kreacher promise to make him drink it all.

"Master Regulus, in," Kreacher's frightened voice said, spindly little hand patting his chest, and he sucked in another lungful of air.

If he could just – if his mind would just stop.

"Out," Kreacher said. He breathed out.

One part of him looked at Kreacher with glazed eyes, and another saw Sirius, instead, the day he'd left Grimmauld.

"You're the Black heir now," the memory said.

Regulus shook his head. "No, no. I don't want it, please, don't –"

"You'll just have to play your part, Reg," memory-Sirius said. "Only one of us gets to do as he wishes, and it looks like it's me."

"Take me with you!" Regulus shouted, twisting angrily. He didn't notice that he'd knocked Kreacher aside. He only saw Sirius, now.

"Please, please, Siri, I can't –"

"You can and you will," the vision growled at him. "If mummy and daddy ask, you'll take the Mark without a whimper, won't you?"

"Yes!" Regulus sobbed, "I will, I did, but –"

"No takebacks," Sirius jeered. "Don't come crying to the Light with that nasty thing on your arm."

Regulus gulped in air, still crying.

"I'll – I'll do anything, Siri," he said, shuddering in between sobs. "Look, I'm – I'm killing him, see? I'm on your side."

"Didn't see you on my side when mum and dad kicked me out," Sirius sneered at him. "Wasn't good enough for you then, huh?"

"No, no, I – I was just a kid," Regulus said, desperately, trying to crawl closer to his brother.

He was getting too close to the water, and Kreacher reached out to pull him back. Regulus didn't fight, but he was past recognizing the house-elf.

"I was scared, Siri," he begged the spectre of his brother to understand. "I wanted to say something, please – please, believe me!"

"Poor little Regulus," Sirius taunted, in a cruel, sing-song fashion, "just wanted to please mummy and daddy, because Sirius broke all the rules and made them mad."

"Don't call me that," Regulus said, angrily. "You've never called me that."

"But it's your name," Sirius said, leaning in and hissing it into his ear, "Regulus."

"You call me Reg," Regulus protested, "you – you're my brother, you always call me Reg."

"Not anymore. Remember? Mum burnt me off the wall."

"I didn't want her to," Regulus cried. "I didn't."

"Lies. You didn't even miss me. Remember what you tried to replace me with?"

Regulus couldn't say anything. He trembled, waiting for Sirius to say it.

"A cat," Sirius laughed cruelly. "Mum got a little cat and put a little collar on it, and do you remember what she called it?"

Regulus shivered violently. He shook his head. "No, don't. Don't say it, please – "

"Orion," Sirius said gleefully. "And you loved it. Remember? You let it sleep on your bed."

"It was just a cat!"

"Mum had you put it in a seat at the table," his eyes were dancing wildly, "in my old seat."

"That was – that was mum."

"You talked to it all the time," Sirius continued mercilessly. "Might as well have added it to the family tree in my place."

"I just, Siri – the cat wasn't a replacement," he swallowed back another sob, "Siri, you left me, I – I was alone."

"As you should be."

Regulus looked at up at him, quiet whimpers dragging out of him.

"No, Siri, no, what are you – "

Sirius smiled slowly, almost kindly. Regulus leaned forward, desperately, his robes nearly touching the water. Kreacher was holding him back with both arms now, but he paid no mind.

"Don't try to pretend, Reg," Sirius said softly. "You know you'll never be good enough for me. It's just who you are: a pathetic little coward."

The hope that had bloomed across Regulus' face a moment ago crumpled into devastation at Sirius' words, but he kept his eyes on his brother, as if he would change his mind, tell him he was joking. Sirius did like to joke.

It said nothing more, however, just smiling as it slowly evaporated into nothingness.

Regulus collapsed back, nearly crushing Kreacher, who leapt back just in time.

"Master Regulus?"

There was no response except renewed sobbing. Regulus curled himself up on the cold stone and cried.

Kreacher stood next to him, wringing his hands anxiously.

Eventually, Regulus came back to himself.

"Kreacher," he croaked, not moving from the ground. "The potion. I drank it all?"

"Yes, Master Regulus. Every drop, even if it hurts," Kreacher parroted back the promise he'd made him give.

Regulus moved, then, slowly lifting himself up off the floor. Kreacher watched him with large, frightened eyes as he took one staggering step, then two, and braced himself against the edge of the basin.

In the bottom sat a locket.

Regulus saw the insignia and laughed. "You arrogant bastard."

He lifted it up out of the basin by its chain and it glimmered in the odd light of the cave. Kreacher stood by quietly, but there was fear in his eyes as he watched his master drop the locket in his pocket, and then cover their tracks.

"Kreacher doesn't like it," the loyal house-elf spoke up as they exited the cave.

Regulus looked down at Kreacher, opened his mouth, and then clutched at his left arm with a quiet gasp of pain.

"You're right, Kreacher, it's very bad," he said at last, "and I need to ask you to destroy it for me."

Kreacher looked up at his Regulus with awe as he handed him the locket.

"Kreacher would be honored," he said, accepting the locket from his master gratefully.

"Good," said Regulus, wincing again as his arm twinged. "I have places to be."

"Master should rest," Kreacher grumbled. Regulus shook his head and looked down at him with a slightly unfocused expression.

"Can't run from this," he said. "Kreacher, just – there's one more thing…"

"Anything for Master Regulus."

"Feed the cat, if it comes back around?"

Then Regulus turned, vanishing with a crack. Kreacher looked bewildered at the empty space.

"Potion went to his head," Kreacher decided, nodding to himself. "Cat's been dead for years."