He's lucid enough to hold his breath as he is dragged into the water, but not lucid enough to open his eyes or fight back. That is until his lungs begin to burn, and he registers that the pain in his leg is coming for the hand tightly wrapped around his ankle. Panic grips his chest, along with the need for oxygen. His eyes peel open, a wave of panic threatens to drown him faster than the water around him.
A face destroyed by the unforgiving water stares back at him. It's sorta funny, he thought he had been afraid before he opened his eyes; the emotion gripping him is so much more than fear. He thrashes and manages to release himself from the chain made of hands around his ankle. He kicks with all his might upwards.
"Regulus, I'm not going to let you drown."
He calls out Sirius's name in surprise. A dumb move considering his lungs are already burning, and the voice is coming from his head and not his brother. However, maybe not. Maybe Sirius is coming to save him. His vision might be blackening, but if he squints he can see the faint outline of him. Regulus tells him he's scared before remembering he is supposed to be holding his breath. Sirius gives him a look. The same look he always gives when Regulus tells him he's scared. Regulus misses that look.
"Hey, I wouldn't let anything happen to you. Alright?" Soft and reassuring the words float out of his mouth
He blinks, Sirius looks 12, not the 21 he supposed to. For some reason, this doesn't bother him as much as he faintly thinks it should. He sounds younger too.
"Here," Sirius takes his hands, "we'll jump in together! Take a deep breath, kay?"
Sirius wouldn't let anything bad happen to him. So he listens. He takes a deep breath, but that only makes the pain in his chest worse. They jump into the water, but, wait. He was already in the water, wasn't he? He's confused. Sirius said nothing bad would happen. Sirius wouldn't lie, not to him.
It takes longer than it should for his brain to clear, but it does. His brother leaves him for a second time. For a second time, he doesn't go with him when he should. Regulus stays in the dark. He deserves it.
"It's okay." He knows he shouldn't be letting the words float out of his mouth into the water; he doesn't care, "I fixed it. I fixed it, Sirius."
He would bet his life, that it was Sirius's voice that replied a soft, "I know"
Everything goes black, and Regulus lets the hands drag him down.