“Bring me the dittany, Kreacher.”
“Mistress said Kreacher was not to help filthy traitorous son-”
“She never said anything about helping me.” Regulus calmly pulled a knife out of his pocket and jerked it across his palm. “I cut myself. Bring me the dittany.”
Kreacher ducked his head and popped out of the room.
“You shouldn't do that,” Sirius groaned from the bed. “It hardly matters.”
“I'll do what I like. Black blood is too valuable to leave all over the sheets.”
“That's why you're dripping it on the floor, then?” Sirius shook his head, then winced. “You shouldn't risk them finding out you helped me.”
“I'm not helping you,” Regulus drawled, the picture of a bored aristocrat. “I slipped with my letter opener and I am waiting for my house elf to bring me the dittany.”
Kreacher chose that moment to pop back into the room, holding a large bottle that he wordlessly held out to Regulus. Regulus took it and nodded sharply at him. “You are dismissed, Kreacher.” The elf popped out again with a subservient bow of the head.
Regulus opened the bottle and poured a little into the palm of his hand, watching the cut seal itself into a thin white scar.
Sirius made a pained noise from the bed. “Only planning to use it on yourself, then?”
Regulus’s lips twisted. “That’s what I said. Really, doesn’t anyone believe me these days?”
“I don’t know why anyone would,” Sirius tried to scoff, but his throat caught mid-word and he started coughing, more blood dotting the pillow in front of him.
Regulus sneered with practiced disdain. “Those pillows deserve better.” He moved to kneel at the side of the bed and poured a thin line of dittany onto Sirius’s back. The blood covering it smoked faintly as the cuts sealed themselves under it. Sirius swore into the pillow, gasping out imprecations on Regulus’s breeding in between coughs. Regulus continued carefully covering his back with the dittany, undeterred. “You do realize that, as my brother, if I am the son of a squib and a whore, so are you?”
Sirius responded with an even more virulent string of profanity that was cut off by an even worse coughing fit. Regulus frowned and set the dittany down on the nightstand. There wasn’t any sense in healing the outside if he was bleeding out internally. He retrieved Sirius’s wand from his pocket - he always snitched it from where Orion locked it away, and if the healing spells were cast with Sirius’s own wand, it was that much less likely Regulus would get in trouble for them - and cast a few diagnosis charms. His composure broke enough to swear.
Sirius went very still. “It’s bad, isn’t it,” he whispered hoarsely.
“Bad enough,” Regulus snapped. “Stop trying to talk, half your lung’s shredded, you stupid wanker. Every time you cough you’re making it worse.” He bit his lip. He didn’t know the incantations for healing this, but he couldn’t go look them up, and if it wasn’t fixed, Sirius was going to suffocate in his own blood within the hour.
He did remember the incantation for removing fluid buildup from within the lungs, and that probably worked on blood as well, so he cast it, following it with another diagnosis charm without pausing for breath.
The diagnosis charm showed that the lung was emptied, and Regulus could keep him from suffocating like this - but then he’d bleed to death instead. He swore under his breath.
Any spell not meant for the purpose that he tried to use would do more harm than good. Lungs were delicate tissue. Any spells intended for flesh wounds would merely fill the lung with scar tissue, and Sirius would struggle for breath the rest of his life - however long that might be. Regulus hadn’t learned the spells for organ injuries yet, they were too rare - he could staunch internal bleeding from an artery, but that too would render the lung useless for breath.
“Sirius?” He could hear his brother’s breath bubbling in his throat, slow and unsteady. “Siri, can you hear me?”
“Mm. Gonna take a nap, Reggie,” Sirius slurred. His hand twitched, like he was intending to wave it dismissively. “Wake me for dinner.” His breathing was slowing and getting rougher.
Regulus bit his lip. This was… this was beyond his ability to fix. Even if the proper incantations were in the family library - which was no guarantee, as the books at Grimmauld Place were much more focused on causing harm than on alleviating it - he had no way to get in. Their parents had kept strict control over the books since Sirius had been sorted, and Kreacher was under orders not to get either of them so much as a single page without telling their father.
If Regulus walked out of this room right now, Sirius would drown on blood and die in his sleep. If Regulus sat here and siphoned the blood out of his lungs all night, Sirius would bleed dry and never wake up.
Regulus closed his eyes for a long moment. It had been years since they could pretend to understand one another, but this would be irreversible. For all that Sirius was treated as a blood traitor, he was still a Black. He was still Regulus’s brother. For all that had gone on in the years since he went to Hogwarts, Sirius had never stopped being his brother.
There wasn’t much use in having a dead brother, even if he wasn’t disowned. Regulus opened his eyes and looked down at Sirius’s face, the dark purple bruises blooming over the sharp cheekbones, the hollows of the eyes, the brittle knife edges of it. He was pale under the bruises, too pale. Regulus leaned forward and pressed his lips to Sirius’s temple, in a spot clear of bruising. Sirius gave a bubbling sigh, pressing into the touch.
“Love you, Siri,” Regulus whispered. “I’ll miss you. I’ve missed you for years, but it’ll be worse now.”
He straightened his spine and called for Kreacher, who appeared with a pop, cringing.
“Kreacher, you will take this out of our house and dump it on the steps of St. Mungo’s. If anyone asks you, Sirius ordered you to take him. Do you understand?”
“Mistress is distaff. I am heir to the House of Black. You will do this for me, Kreacher, and the blood traitor will never darken our halls again. Do you understand?”
“Yes, master Regulus.” Kreacher bowed, his ears brushing the floor. “Kreacher will take out the filth, and then Kreacher will punish himself for aiding the blood traitor, but he was dirtying Mistress’s linens, and Kreacher wanted his filth gone.”
Regulus smiled, a thin, cold smile with nothing of pleasure or humor in it. “Very good, Kreacher. You have always been a loyal servant.”
Kreacher ducked his head again and stepped forward to lift Sirius from the bed, then vanished with a crack.