Work Text:
The way Gabriel justifies taking a side in this stupid war is this: if Dad doesn't want him to join Team Free Will, He wouldn't have given Sam Winchester a smile that looks like that.
Not that he'll ever explain that to anyone else. As far as the rest of the world knows, he's joined the Winchester's because they're the only side that don't need an urgent sense of humour transplant.
The first time Gabriel sees Sam smile, really smile, like he could be mistaken for the happiest person on the planet, it hits him so hard that he almost flickers into the visible spectrum. The three of them, Castiel and the Winchester brothers, are in yet another crappy diner discussing the monster of the week that they've come to take care of (they're completely off base but as far as Gabriel can tell that's just going to make the resultant clusterfuck all the more fun to watch).
One moment, Gabriel's watching from the side-lines, invisible and undetectable, as Dean tries to convince Cas to eat. The next, Cas has made some comment prompted by his complete and utter bafflement at human kind. Dean, caught off guard, actually laughs and Sam grins at both of them.
For Gabriel it's like the sun's come up. Like the first time he'd looked at Adam and seen the flash of his Father's Grace.
After that he doesn't follow them for fun anymore. He follows them hoping to catch another glimpse of that smile and more and more often he finds himself helping. Just a book or a weapon in the right place at the right time or a timely distraction, things that can be shrugged off as coincidence, for no other reason than that it might make Sam happy.
He's glad no-one can track him because he's uncomfortably aware that he's acting like a love-sick puppy. It's depressing, even more so because he can't make himself stop.
When Gabriel finally shows himself, and declares his loyalties at the same time, it's to stop Zachariah's blade from skewering Sam. The angelic, middle-management, douchebag turns up when Castiel is off on one of his useless searches for Daddy and Gabriel watches with horrified certainty. Knowing, as a shouting Dean is restrained, that this is it; the moment he has to make a decision.
It turns out it's not much of a decision at all and as he catches the down stroke of the blade against his own he's stupidly relieved that, of all his brother's, the first one to feel his wrath is Zachariah. This death he won't feel that guilty about, especially since it's to save Sam.
The look on Zachariah's face, as his blade is knocked aside and Gabriel stabs him through the chest and twists, is one that he tries not to think about too much, all the same. Gabriel replaces the memory with the brilliant sight of Dean gaping at him completely poleaxed and with the happy, proud look Castiel gives him when he finds out that Gabriel's joined his side and with Sam, looking at him with an expression of surprised awe and wonder that he'll never forget.
The second time Gabriel sees that smile, the one that Sam hides so that anyone who's never seen it would never know it's there, it's once again directed at Dean and Castiel and for a moment it makes Gabriel so jealous he can't see straight. When he's wrestled back control of his emotions Cas is giving him a head-tilted look that's got far too much knowing in it and not enough confusion for Gabriel's liking. He steps up his attempts to make Sam smile anyway. Correcting for the new data set and ignoring Castiel's sympathy as best he can.
In keeping with his previous dealings with the Winchesters, when Sam finally smiles at him, he's not expecting it. It catches him by surprise and all he can do is stare as Sam laughs; the man, for a moment, so happy and carefree, as if the world isn't dying and they aren't living on borrowed time. It's contagious and when Sam's eyes meet his, he beams back without consciously making a decision to. For once, he doesn't think about what emotions are showing on his face or what the best response would be to achieve what he wants; he just smiles.
It's only when Sam's smile gets even wider and brighter, which Gabriel hadn't thought possible, that the Archangel realises that maybe Sam was searching for Gabriel's smile too.