It took only a few weeks after Castiel had fallen for him to realize that he had an oral fixation. At first it all seemed to make sense, to him at least; humans were supposed to have an instinctual need to eat, right? To have things in their mouth? But usually that need came with the need to swallow, and outside of mealtimes Cas never felt that need. He just needed something in his mouth, occupying the empty space. He needed his mouth to be busy constantly, otherwise he got jittery and annoying.
Dean joked that it was because Cas was never breast-fed, and now that he was human all those psychological needs were kicking in late. Cas didn't really care about the reason, though. He walked around with a lollipop in his mouth for almost a whole week until he'd choked on it on a case and decided to break that habit for his own safety. He'd even had a brief thumb-sucking phase, which ended soon after "Damnit Cas, babies do that!" It wasn't enough, anyway. He needed something bigger.
"Fuck," Dean hissed as Cas ran his tongue up Dean's thigh. He worked Dean's underwear down, eyes locking on the large member that sprang free. It wasn't the first time Cas had seen Dean in all his naked glory, but it was the first time he'd ever considered doing this.
He flicked his tongue over the head of Dean's cock and instantly groaned as Dean wrapped his fingers tight in his hair and pulled. Castiel grabbed Dean by his hips and held him in place as his lips wrapped around the hunter's length and sank down, taking him into his mouth.
He couldn't stop his eyes from rolling back as Dean's cock filled him so perfectly. He groaned around the thick length and took another inch, feeling the head press against the back of his throat. He waited to feel his gag reflex kick in but nothing happened; just Dean pulling him forward a little, working his cock in deeper, and Cas moaning against him, sending vibrations shooting through his erection.
Castiel pulled off with a lot 'pop' and sucked along the underside of Dean's shaft, licking spit and precome up, before taking him back in his mouth, this time deeper than before. Just as he'd suspected he didn't gag. He smirked slightly, took a deep breath, and pushed forward until his lips were tickled by the trimmed hair surrounding Dean's member and Dean's cock was in Cas' throat.
"Holy hell!" Dean's head fell forward, eyes clouded by lust, as Cas swallowed around his length. Castiel's eyebrows pulled together but he decided to ignore Dean's odd word choice in favor of bobbing his head back and forth.
"Oh fuck, oh fuck, Cas..."
Dean tightened his fingers in Cas' hair, sending shivers down his spine. He had never had something so big filling him up; it felt too good to be true, like Dean's cock had been made just for his mouth, just for him to taste and suck and swallow around. Cas pulled off again, and only when his head felt fuzzy and his vision blurred did he remember that he had to breathe.
"Careful..." Dean warned, though he could hardly think about anything besides the tight channel of Cas' mouth. He kept pulling Cas' head forward, giving Cas an idea. Cas looked up at him with wide, innocent eyes.
"Dean, fuck my mouth."
Dean blinked rapidly. "You're joking, right?"
"Do I look like I'm joking?" Cas let his tongue circle the head of Dean's cock before dipping into the slit, and he watched as Dean's muscles strained at the touch. A drop of precome collected at the tip and Cas swiped it away.
"Oh my god," Dean shuddered. He placed one hand firmly on the back of Castiel's head, the other lightly tracing his shoulder, and Cas opened wide for Dean's cock. In one swift motion his cock was in his throat and Cas groaned, knowing the sensation would go right through the head.
"Son of a..."
Dean pumped his hips forward slowly, getting Cas used to giving up power and trusting Dean to do this to him. Every few seconds he pulled his cock out enough for Cas to take a deep breath before he pushed in again, slowly picking up the pace until he was fucking Cas' mouth relentlessly.
"Fuck, Cas, you like it when I use your slutty little mouth? Like havin' a fat cock down your throat? Ah..."
Cas' groans got louder and more frequent, producing these beautiful gagging noises that made Dean want to come right down his throat and force him to swallow every last drop. For his part, Cas had never been happier. He was completely satisfied with Dean using his mouth like this, like he owned him, and Cas' oral fixation was loving every minute of it.
"Fuck, fuck, Cas, gonna come-"
Cas reached around and dug his nails into Dean's firm ass, and Dean's hips shot forward, cock pushing almost too deep, before he stilled and came down Cas' throat. Cas moaned, and his whole body suddenly tightened and released; he was so preoccupied with Dean's pleasure that he didn't even realize how on edge he was without even touching himself. He gasped around Dean's cock, throat working to swallow his cum, until Dean pulled down and filled Cas' mouth with the last of his seed, leaving a trail running down his chin.
"Shit, Cas..." Dean fell to his knees, legs shaking and chest heaving, as Cas swallowed his load and licked the trail off his chin. Cas felt so buzzed, so high off everything. He leaned his weight on Dean's shoulder as Dean engulfed him in a tight embrace.
"M'sorry, Cas, totally forgot about you-"
Dean looked down, half looking like he was going to burst out laughing and half incredibly pleased with himself, eyes roaming over Cas' cum-covered thighs and abdomen.
"Shut up," Cas laughed. His throat sounded a bit croaky and he was sure Sam would notice immediately, but he couldn't be bothered to care. He was already looking forward to the next time.