Author Note: Just a little something that had been buzzing around my head. Sirius's POV is really hard for me, so this is not my best writing...
Sirius Black walked down the noisy corridor. His thoughts were not on his friends who stood laughing and talking beside him. James must have just said something funny because Peter was nearly falling over with laughter.
"Easy there James, you don't want to kill Wormtail with your humor." Remus joked. The other boy wiped his watery eyes on the sleeve of his robes and reigned in the laughing fit. Sirius normally would have teased Peter. Perhaps said something about him being in love with James and that was why he was acting like that. But his mind wasn't on them right now.
His mind was on his brother. Little Regulus: his parents' favorite child. It was not jealousy that colored these thoughts. They were even free from the stain of disdain he usually felt when thinking about his brother. No, it was concern.
As they rounded a corner they passed a bunch of Slytherin boys, standing in a circle and whispering animatedly. A handsome boy with shoulder-length black hair was standing among them. His face glowed with excitement. Regulus was among the people James referred to as the Future Death Eaters Club. Sirius's stomach dropped to his feet. How could his little brother be so stupid? How could he think that this was the right side to be on?
Two of the older boys looked up and gave the Marauders a dirty look when they walked by. The two groups had been enemies since the very first day at Hogwarts. A boy their own age with greasy black hair was eyeing James with a particular loathing.
"Oi, Snivelus!" James called, "Don't make us give you another bath in the lake. Were you really born that greasy?" He looked to Sirius with a grin, hoping for another good joke at Snape's expense. Sirius only smiled half-heartedly, still staring at Regulus's back.
Maybe his brother wouldn't be with those Slytherins if he had been more supportive of him. Maybe he could have spent less time fighting with his brother and more time talking to him. Could he have stopped his brother from doing this? Could he stop him still?
Night was falling and everyone was heading back to their Common Rooms. James, Remus, and Peter had gone on ahead. Sirius had told them that he had left something on the Grounds. Really he just needed to see something. He had to check. The black haired boy stepped behind a column near the way to the Slytherin Common Room. No one approaching could see him.
Regulus was walking by himself. This made it much easier for Sirius. Stepping out from behind the column, he passed his little brother on his left side. His heart was thumping wildly in his chest. What if Regulus had it? What would he do then?
Sirius grabbed Regulus's arm when they passed each other and violently ripped up the left sleeve. All that was there was clean skin. Perfectly pale skin that was clear of any signs of evil or darkness. Regulus jerked his arm back and glared at his older brother.
"What was that for?" he snapped. Sirius didn't respond. His brother had not taken the Dark Mark. Not yet at least. Sometimes, seeing nothing was better.