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When the question finally comes up, Dean is so not prepared. They're sitting in the library with Sam, for Christ's sake, reading up on some case in Idaho, when Cas carefully closes the book on his lap and turns to face him. He's got that look on his face, the one that means trouble. Dean sits up in his chair and steels himself for whatever weird-ass comment the angel's about to hit him with.
"What's up, buddy?"
Cas blinks a few times, then purses his lips and looks away. He seems conflicted, which is hardly a new look on the guy, but it still worries him nonetheless.
"Hey, man," Sam peers around his laptop with a frown. "You okay?"
Dean glances at his brother, then back at Cas.
"Well, c'mon then. Spit it out."
Cas scrunches his nose up a little, his angel brain probably taking the request too literally. When he turns back to face him, his eyes are bright, but weary.
"Dean… Why do you call me sunshine?"
Sam tries to hide his grin behind his arm, but Dean can still see his shoulders shaking with laughter as he turns back to his research. His cheeks instantly warm with shocked embarrassment.
"Uh, what?"
"You call me sunshine," Cas says with more confidence now. "Every morning when you make me coffee, and just before you go to bed at night. You call me sunshine."
Dean clears his throat and shrugs, a little lost for words. "It's just a, uh… It's just a thing, ya know? Like a nickname. Nothing important."
"But what does it mean exactly? My position in heaven had nothing to do with controlling the sun."
Sam full on snorts, which earns him a glare.
"It's not literally about the sun, you idiot," He grits out, but his words sound more tired than angry.
"Then why -"
"Geez! Just drop it, will ya?"
"No. Go on, Dean. Tell us what it means," Sam closes the lid of his laptop and leans forward, beaming like a child at story time. "I really wanna know."
He gives his bitch of a brother the best scowl he can muster, then scrubs a hand over his face and turns back to Cas. The poor guy is frowning down at his hands, looking like a scolded puppy.
"It's like a metaphor," He swallows thickly, waiting for Cas to meet his eyes before carrying on. "Cos, ya know… the sun makes everything brighter and stuff."
Cas tilts his head to the side, in that oh so typical confused angel kind of way. It floods his chest with warmth, and he can't help but smile softly as Cas slowly tries to wrap his head around the explanation. He knows he's not off the hook just yet, but he still allows himself to enjoy the adorable expression on the guy's face.
"So, you're saying I… make things brighter?"
"And stuff," Sam adds with a grin.
"Shut up, Sammy."
"What? I'm just repeating your words, Dean. Tell me, what kind of other stuff does the sun do?"
He rolls his eyes, then catches Cas' hopeful expression. He's actually waiting for him to elaborate, for crying out loud. Where the hell does he go from here?
"Aren't angels supposed to know this sort of thing?" He massages his temples wearily. "Photosynthesis and all that jazz?"
"Oh, that's not my doing," Cas says earnestly. "The plants do that all by themselves. They're very remarkable organisms actually."
Dean throws his head back in surrender and fully turns in his chair, pointedly ignoring the poorly suppressed laughter coming from Sam's end of the table as he gets Cas' attention again.
"It's a term of endearment, okay?" He blurts out. "I call you sunshine cos, I dunno… when I'm feeling down, you make everything seem better. Like, the sun comes out and… drives out the darkness. Look, I'm not a frickin' poet, alright? Just - just leave it at that."
He quickly dives back into his research to avoid the knowing look in Cas' eyes. Even Sam has stopped laughing, which pretty much says it all. He just wore his heart on his sleeve - big time. If it wasn't obvious before, it sure as heck is now. And all because he slipped up that one time, calling Cas by that stupid name out of the blue. He doesn't even know where it came from, but it just sorta stuck over the years. Cas never mentioned it, so he thought he was safe, but obviously not. You can't hide your feelings forever it seems.
"Dean," Cas says softly after a while, prompting him to look up. Just as he feared, there's that strange look in those big blue eyes of his, like he just heard a secret and doesn't know what to do with it.
He rubs at the back of his neck to hide his blush. "What?"
Cas smiles - all wide and gummy and frickin' adorable - then reaches forward to take his hand. The unexpected contact is enough to send sparks tingling up his arm.
"Thank you," He ducks his head bashfully, fingers tightening in his grip.
"Oh," Dean blinks dumbly. "Uh, yeah. Sure. No problem, I guess."
He tries to pull away, to discreetly move on from a potentially awkward conversation, but Cas stops him. His eyes are glowing this gorgeous, ethereal blue, and the softest of smiles is touching his lips. Dean has never wanted to kiss him so badly before in his life.
"You're my sunshine, Dean," He says with no ounce of insincerity in his words - just pure, genuine adoration.
Dean allows himself a smile as he squeezes Cas' hand. "Yeah. Uh… same. You too, I mean."
They stay locked in each other's gaze for a moment longer, before Sam leans across the table - like the infamous cock-block he is - and bats his eyelashes.
"Aw, Dean. Can I be your sunshine, too?"
"Screw you," He grumbles, shoving his brother back into his chair.
They return to the case without another word, slowly slipping back into the same old routine. Nothing has really changed. It's almost like the past ten minutes didn't even happen. Only, Dean knows that's not entirely true, because he can still feel Cas' fingers laced between his own. It's not a big deal, but it makes all the difference.
For once, he can just breathe.