What about a fic set during a stretch of time where Sam and Dean are just hunting non-stop, heads down, focused on the family business? They get into this rhythm, working in tandem where they barely even speak, all body language and intuition.
After one particularly gruelling hunt that has had them on their feet for days, battered and exhausted, they get back to the motel and are simultaneously bone-tired and yet fully wired on the post-hunt adrenaline. Dean near collapses on the end one bed, head hanging, hands propping himself up on his knees. And silently Sam comes to him, like a magnet drawn to iron, kneeling down and starting on Dean’s boot laces.
There is no rush, nothing uttered just familiar hands working at well-worn clothes, easing each item off one at a time. When Sam makes it to Dean’s belt buckle though there is something new. Dean huffs a breath out, almost pained, and when Sam looks up he can see the pink on his brother’s cheeks. Dean can’t meet Sam’s eyes, so he closes them instead. His tiredness is contradicted by his tented jeans, the racing pulse Sam finds under his touch.
It takes Sam less than a minute to decide something he hasn’t ever really considered. Dean needs him and that’s good enough for Sam. The sound of the belt buckle clinking and the zipper undoing must knock Dean back into the present, but instead of seeing revulsion or fear in his eyes, Sam sees warmth, wonder, even the hint of a smile on his brother’s lips.
Dean cups Sam’s cheek for a moment, then moves to curl his fingers in his hair—Sam takes this as invitation, sitting up on his heels so he can use the leverage to ease Dean’s jeans off his hips. Dean helps by lifting himself enough to wrestle the pants to his knees.
The strangeness of the situation catches up to them for a beat as they sit, Dean nude from the waist down, cock standing at attention mere inches from Sam, still in his jacket and boots as if ready to head out any moment. But the look on Sam’s face is something like determination, something like admiration Dean thinks. Whatever it is, the fear biting at his heels is quickly quashed and he feels the heat of Sam’s mouth envelopeing his cock before he can even think of anything disarming to say. Sometimes there aren’t words for whatever they have going on and that’s okay. Better than okay.