AN: I'm taking a few liberties with this story, like making Sirius an auror and having him find about Regulus' death while he's in Azkaban. Just so you know.
I don't own the characters. If I did you can be damn sure Sirius would still be alive.
Sirius raised his lit wand as high as he could, looking for any sign of his partner. The light didn't help much: it extended about three feet before it was swallowed by the inky blackness.
"Thompkins! Thompkins!" Sirius whispered. There was no answer.
Sirius sighed. He had warned the idiot that charging off down a tunnel underneath a Death Eater's house wasn't a good idea, but did he listen? Of course not! It's not like I know anything about Dark wizards and what they're capable of, Sirius thought to himself sarcastically. It's not like I got top marks in my training or anything. Why on Earth would Thompkins ever listen to me?
Deciding that monologue-ing in his head wasn't getting him anywhere, Sirius set off down the tunnel, keeping his eyes peeled for any sign of movement. He wondered, yet again, if joining the Auror Office right after school had been a mistake.
James had certainly been surprised when Sirius announced his plans. "Are you sure that's what you want, Sirius? Now that we're done with school and you're finally free of your stupid family, I thought you would want to live it up for a couple years and have a good time, like me!" That was a lie, he wasn't having a good time, none of them were; they were all too scared. James was just trying to hide the fact that he was worried about his friend, Sirius could tell. Lily had been worried, too, and she had been much more open about it: "But Sirius, being an Auror is so dangerous, what if something happens to you? Are you sure about this?" Pete hadn't said much more than "Wow!" in an awed voice. But Remus, who Sirius always thought was a little too perceptive for his own good, had hit the nail on the head: "Come on, Padfoot, you don't have to do this, you don't have to play the hero. You don't owe anyone."
But that wasn't true. He owed everyone, everyone who was suffering at the hands of Voldemort. Sirius' rotten parents had supported Voldemort and donated to his cause, his cousins had joined the ranks of the Death Eaters. He had to do something to make up for that, to show that he was different.
Your brother joined them, too, a quiet voice whispered in his head.
Enough with the reminiscing, Sirius reprimanded himself as he stepped over a large puddle of what he hoped was water. He needed to find his partner before the twit ran face first into Voldemort.
Sirius picked up the pace, walking for what felt like an hour, eyes and ears straining for the slightest hint of life. Finally he reached a fork in the tunnel and stopped, having no idea which way to go. He was debating sending a Patronus and asking for backup when he heard something down the left hand tunnel.
It almost sounded like whispering.
He set off after it, moving as quickly and as quietly as he could, extinguishing his wand. He was surprised to find that he could see without it, as there seemed to be a faint light coming from the tunnel ahead. The whispering, because that's definitely what it was, had grown just a little bit louder.
Finally Sirius reached the end of the tunnel. It opened into a gigantic room, only slightly smaller than the Great Hall at Hogwarts, but it was empty. Well, almost empty. The light was coming from a lantern in the corner of the room, where a large… something stood draped in a curtain. Whatever it was, it was the source of the whispering.
Well, this doesn't seem suspicious at all, Sirius thought, edging forward carefully. But he couldn't help but be drawn towards the curtain, knowing all the time that he should simply turn around and leave.
But he couldn't. He had to find out what it was.
He strode forward, yanked the curtain off in one smooth movement, and jumped back in alarm as he found someone staring back at him.
He laughed when he realized it was his reflection. The curtain was hiding a gigantic mirror.
He stopped laughing when the reflection began to change.
The face thinned, it shrunk a few inches, and the hair grew to the point where it reached his shoulders. Sirius now found himself looking at his brother, Regulus.
He had just begun to fully absorb this fact when Regulus started to speak.
"Why did you leave me, Sirius?" he asked mournfully. He seemed hurt. "Why did you leave me with our parents? Why did you let them talk me into joining the Death Eaters? Why did you abandon me?"
"I… I…" Sirius stuttered, unable to form words.
"You were my big brother," Regulus interrupted. "You were my hero! You were supposed to protect me!"
"I'm sorry, Reg!" Sirius finally got out. "I'm so sorry, I wanted to take you with me, I did. I tried to protect you..."
"Oh you tried," Regulus said with scorn. He looked furious now. "You tried and you failed. I don't know why I ever looked up to you. You're such a disappointment, Sirius."
And like that, the reflection began to change. The face filled out, the black hair grew longer still, and the voice became high pitched and grating. "Such a disappointment! SUCH A DISAPPOINTMENT!"
The sight of his mother was finally enough to bring Sirius to his senses. Without another glance he turned around and ran.
When he literally bumped into Thompkins later he told him that the left fork of the tunnel was deserted. Thompkins was disappointed and wanted to check it out for himself, but Sirius dragged him away.
Years later, Sirius was having a horrible dream. This wasn't uncommon; after all, he was in Azkaban. But this wasn't one of the usual nightmares. He was walking down a dark tunnel that looked vaguely familiar, and he was trying to find…something. He couldn't remember what. But he was sure that in a minute he would walk into a room and there would be a mirror.
Sure enough, the mirror was still standing in the corner of the empty room, but this time the curtain floated off by itself. Sirius knew that he was going to see something horrible when he looked into the mirror, but walked up to it anyway. He didn't have a choice.
For a minute he blinked stupidly at his reflection. He certainly didn't enjoy looking at himself with matted hair and a gaunt face, but he knew something much worse was coming. Sure enough, his reflection began to change. But it didn't turn into Regulus, like Sirius expected.
It turned into James.
Oh God.
It was worse than when the dementors came around and the image of James and Lily lying dead got played over and over in Sirius' mind. It was worse than when he first realized Peter had betrayed them and his best friends were dead. It was worse than anything he had ever felt before in his life.
And then James started to speak.
"Why did I ever listen to you, Sirius?" He had only ever heard James use a tone like that once before, when he had played that stupid trick on Snape sixth year. "I should never have trusted you. You always mess up everything. I should have known you'd mess this up, too."
Sirius knew what was coming next. Silently he begged, he pleaded with James not to say it.
"It's your fault we're dead."
Sirius had never felt true anguish before.
And then it changed again.
"Our baby is an orphan because of you." Lily said, her face twisted with rage. "It's your fault we're dead."
And then it changed again.
"I can't believe you didn't trust me," Remus said quietly. "After everything we've been through. It's your fault they're dead."
And then it changed again.
"I can't believe I treated you like a son," Mr. Potter said, shaking his head solemnly. "What a mistake that was. It's your fault they're dead."
And then it changed one last time.
"See, Sirius?" Regulus whispered. "I told you. I tried to warn you, but you just wouldn't listen. You're a disappointment, Sirius. And it's your fault we're dead. "
This time Sirius couldn't run.