The Black brothers. Gen. The social atmosphere of Hogwarts is easy to lose yourself in and drown, if you let it happen.
Hogwarts always seems larger than it is, and Lily attributes this to the social atmosphere, something she's never wholly devoted herself to (she claims) but warns the rest of them is easy to lose yourself in and drown. She warns Sirius in particular, "And you know you've got to do something after Hogwarts, yes, even you, so don't let yourself be pulled in. Even you have something to offer, Sirius Black."
"I do?" he responds, peering through his fringe with a wicked grin. She crosses her arms over her chest and tuts, but he regards her words. To some extent.
It's not until a few weeks later that he understands completely, when he sees Regulus in the library as usual, being caught by the shoulder by Rabastan Lestrange. The breath catches in his throat and his eyes won't move from the scene, the heated whispers and finally the shove.
You're a Black, do something, do something, Sirius wills, swallowing and growing angrier every second.
Regulus colors, and responds in a muted whisper - Lestrange gives a little self-righteous smirk and leaves him there, robes mussed and eyes lowered.
Sirius stands and walks the couple hundred feet over, and Regulus's gaze immediately shoots up. "You," he hisses, and takes a step back.
Sirius finds himself unable to approach further, but Regulus was always good at alienating others, raising that invisible wall. "You're - " better than "- pathetic. Since when does a Black get shoved around by a Lestrange?"
Regulus's gaze is hard, but his brown eyes are still large, and soft, like a child's, his eyelashes long and effeminate. "Since a Black is led by a Potter," he says, each word filled to capacity with vitriol.
"You can't do anything without me. Is that why you're playing about with those bastards? Face it, Reg, you - "
Regulus raises his wand in a smooth motion, almost and it's only a few inches from Sirius's face. "Don't. Fucking. Underestimate me."
"You have no one," Sirius says, forcing himself to be quiet. "You have nothing. All that money and pedigree and you have nothing at all."
Regulus's wand hand quivers. "At least I'm not blind."
"No." Sirius's sharp eyes don't leave Regulus's face, and there's only a moment of struggle there before Regulus shoves his wand in his pocket. "You're drowning," Sirius says, before any final shot his brother prepares can even emerge.
Once more color comes to Regulus's face, once more his head drops for a moment and once more he retreats, but this time he manages to look up. His expression is a full admission of guilt.
There is a rare, irresistible urge to wrap his arms around the boy, some form of comfort, but Regulus seems to sense this and takes another step back. "I hate you," he says, picks up his things from the nearby table, and leaves.
Sirius doesn't move, just looks through the shelves. He hears the short, quick steps and sees the stalking posture, and watches Severus Snape for a moment, before turning away, idea bright in his eyes.
Someone has to pay.