Dean startled out of a doze at an insistent knock on his door; Sammy knew it didn't take that much noise to rouse his hunter's reflexes from even a deep sleep, but he was a little brother: determined to be as obnoxious as possible.
"What, bitch?" he demanded after groaning his sore body out of bed to answer the summons.
"You need to go to the library." Sam was obviously trying, and even more obviously failing, to hide a smirk.
Dean stared, waiting for an explanation, but Sam failed to expound on his instruction. "Okay, and why should I do that?"
"I can't tell you," Sam all but giggled.
"Right. Dude, I haven't slept in almost three days and I'm pretty sure that tulpa cracked some ribs. Whatever you're trying to pull can wait until tomorrow."
"No, Dean, it's not a prank. I promise! It's Cas, actually."
"What about Cas?"
Sam looked slightly guilty, but still mostly smug. "He found something in the collections while we were gone. It's nothing dangerous," he hastened to add as Dean frowned in concern, "but I think he wanted to keep it a secret until he could practice more."
Despite a few more insincere grumblings about his need for some good old R&R, Dean was sufficiently intrigued to be drawn out of his room.
"You're not coming?" he asked when Sam turned the opposite direction.
"Nah, I've seen enough," was his brother's ambiguous reply.
Moseying toward the library, Dean vaguely became aware of brassy music drifting through the hallway and wondered if Cas had found an old record player (or some stranger Men-of-Lettersy version). But when he reached the doorway, he realized that wasn't right.
Cas had found a saxophone.
He cradled the tip of the mouthpiece in his mouth, lips parted around reed and plastic to breathe life into the instrument. His fingers, firm and commanding, stroked and pressed over the keys insistently to wring out every last note it could give.
Dean must have made a sound, because the playing abruptly stopped and Cas's head snapped up. He stared at the hunter, blue eyes uncertain, but Dean found himself unable to meet the gaze.
His own attention was focused on Cas's tongue as it darted out to soothe swollen, abused lips.
"Dean?" Cas was nearly breathless, gasping in stuttering lungfuls of air through his still-slack mouth and Dean couldn't tear his eyes away.
Until a drop of sweat, presumably originating at the fallen angel's temple, rolled through Dean's peripheral vision as it traced down the hard line of Cas's jaw and caressed his throat before finally sliding down to pool along his clavicle. Dean followed its path, he had to, and then he was staring at the damp, heaving skin of Castiel's chest exposed through the undone buttons at the top of his white shirt. In an entirely unavoidable moment of revelation, he discovered that the result of Cas's exertions had soaked the shirt through and rendered the fabric translucent across the other man's pectorals.
He was drawn from his study of the dark, textured outlines that could only be Cas's nipples by the man himself with another questioning, "Dean?" His voice was still hesitant, though he was no longer panting as heavily around Dean's name. "Was I disturbing you? I apologize, I'll stop-"
"No!" Dean's overly loud exclamation startled both of them, and he had to cough and scratch the short hairs at the back of his neck before continuing, "I mean, it wasn't bothering me. You should keep, uh, keep playing."
"Oh. Thank you, Dean. I would like to continue practicing. The act of making music is one I watched from afar for all of existence, but I was never permitted to join. Now that I am able to hold an instrument in my own hands and bring forth song from its body, I find the experience to be extremely pleasurable."
"Good." Dean licked his lips and his eyes darted back up to Cas's face, which still held a warm flush from his extremely pleasurable efforts. "That's, yeah, good."
They stared at each other.
"Was there something else?" Cas asked, hands clenching on his saxophone. Small auras of condensation gathered around his fingers where they pressed against the metal. He loosened his grip, fidgeting self-consciously, and the ghost of his touch took long moments to fade away.
"Could I... Do you mind if I watch?"
"You want to watch?" Cas confirmed dubiously.
"Yeah, I'd really like to watch. Listen. If that's okay."
"I think," Cas frowned, considered Dean with his head cocked to one side, then nodded, "I think I might like that, as well. Please don't expect much, though. I'm still not very good."
Dean pulled up one of the high-backed leather chairs, settling a few feet from Cas. He spread his legs, leaned forward on his elbows, and offered a slowly growing smile. "It's okay, Cas, I'm sure I'll love whatever you do. And anyway, it's not like this has to be a one-time thing."
The tentatively eager hope that bloomed across Cas's face was marvelous to behold. "You would do it again?"
"Hell yeah. Whenever you want."
Cas flashed him a quick smile, then looked down at the saxophone and set his shoulders in concentration. Still, when his lips parted to welcome the instrument's slide into his warm and willing mouth, his eyes were locked with Dean's.