The first time Regulus hears their word, he’s 10 years old.
“We should have a word.” Sirius suggests to him on a clear, starry night. Sneaking onto the roof of Grimmauld place was a nightly habit at this point, being easy to access and hard for their parents to monitor. Regulus glances at him, pulling his eyes away from the bright star he was observing. “Something sort of… random. Or obscure.”
“Sorry, what?” Regulus interrupts him. Sirius’s odd trains of thought often confused him.
Sirius continues, “Like, a word that Mum and Dad don’t know the meaning of. To mean… you know. That we’ll be there for each other, or we’ll get out of here. Something like that.” Despite Regulus’s gaze being intently on him, his eyes didn’t stray from the sky.
Regulus’s thoughts drift to earlier that same day, during his piano lesson. Sirius, as usual, had stood next to him with his violin, and his parents had been berating him for some reason or another that Regulus couldn’t quite remember. When the sound of a slap echoed around the high-ceilinged room, Regulus desperately wanted to get up and pull his big brother off of the floor. But something kept him stuck to the bench, something that wasn’t imperio or anything magical. Something like fear.
Instead, he dared to glance down at Sirius, gray meeting gray as silent understanding passed between them. There was no resentment to be had, although Regulus thinks there should have been.
He thinks for a moment, and responds, “Tchaikovsky.” It was his favorite composer out of the few that Walburga and Orion allowed in the house.
Sirius nods, a slightly mischievous grin taking over his face. “Perfect! Mum and Dad will just think we’re talking about Swan Lake, or lessons, Reggie, that is brilliant! See I knew there were reasons we kept you around. James says…”
Regulus feels safer than he did minutes ago, letting the starlight fall behind his eyelids as he drifts off.
—-------------
Five years older, Regulus stands in his brother's doorway with tears threatening to spill out of his eyes.
Minutes ago, he had been sitting at the dining room table with the rest of his family. Sirius attempting to provoke his parents was nothing new, obviously, but tonight it had resulted in something particularly ugly between them that ended with Sirius abruptly standing up and going to his room.
This in itself was not what made Regulus feel like the floor was being yanked out from under his feet. That was thanks to the fact that Sirius was digging his broom out from under a pile of dirty clothes and lacing up the muggle-manufactured boots that Remus had given him for his birthday.
Regulus shakily breathes in. A voice in his head (that sounds suspiciously like his mother’s) demands him not to cry. “Sirius?”
His brother jumps a bit, turning quickly to look at him. His eyes soften infinitesimally, but Regulus notices. He whispers, “Where are you going?”
For a moment, Regulus thinks he sees Sirius question himself, which he rarely does. However, he must ignore it in the end, answering softly, “To James’s. I can’t stay here, Reggie.”
Regulus' breathing picks up again, and he walks to Sirius, stepping over piles of clothing and quidditch magazines. His brother has a crease between his brows, following his steps wearily. He opens his mouth, presumably to ask what he’s doing, but before he can get the words out there are two pale arms wrapping around his body and a face being buried into his shoulder.
“Please don’t,” Regulus whispers, trying not to completely break down. “Don’t leave me behind here. You know- you know what’ll happen if I’m the only one. You do. Don’t– Please– Tchaikovsky, remember? Please–”
Sirius hugs him back, pressing his cheek into Regulus’s hair. His baby brother. Always his baby brother. “You can come with me, Reg.” He softly says.
“They’ll come for the both of us if I do. At least wait until I age out, please.” He knows he’s begging at this point, his breaths coming faster and faster, desperate to not be left behind.
Sirius wills himself to let go and look Regulus in the eye. “I can’t. I love you.”
Regulus can’t say it back.
He feels himself drift away from his body as he follows Sirius to the door, then out onto the porch. He mounts his broom and turns to Regulus with teary eyes. He only says one thing before he goes.
“Tchaikovsky.”
By the time Regulus is reaching out for him, he’s gone.
—---------------
Regulus is eighteen, standing on the edge of a rock overlooking gray, angry saltwater. There’s a gold locket hanging around his neck, and he knows what he must do.
If he looks hard enough, he can just make out pale forms below the surface of the water. He gives the locket a small tug. If there was one thing his governess never taught him, it was how to prepare to drown himself.
He backs up from the edge, just a bit. His brain supplies him with a nice memory, one of the many vacations he and his family took to France when he was young. He remembers sneaking off in the early morning to explore with Sirius, and finding a short cliff over a clear, small reservoir.
Sirius gave him a look, a mischievous grin that Regulus knew well, before jumping straight in. When he yells for Regulus to follow, he backs up, breathes in, and jumps as high as he can get, laughing with excitement as he falls into the water.
When Regulus backs up and jumps this time, he thinks he hears his brother inviting him to. He hears the laughter, feels the sun on his head.
When he hits the water, he hears “Tchaikovsky.” for the last time, and the hands clawing at him feel like his brothers embrace.