The first time Dean sees Castiel it is in the abandoned warehouse, with protective sigils from every language and culture they can think of scrawled on the walls and floor and a vast array of weapons on the table.
When Bobby performs the ritual to summon whatever the hell Castiel is he waits with weapons drawn and ready, because he knows nothing would just help him. There was always a price to be paid or a sacrifice to be made.
The first time Dean sees Castiel he sees him as a threat. Sparks rain down around the thing's form as it enters accompanied by the howling of the wind. It doesn't stop when he shoots it; doesn't even flinch when he drives a knife into its chest.
Deadpan, it intercepts Bobby's crowbar. With just a touch of its fingers and not even a hint of concern it makes Bobby fall to the ground, barely taking its eyes off Dean the entire time.
The first time Dean sees Castiel he sees him not as a man, but a monster.
The first time Castiel sees Dean it is in the depths of Hell, every inch of his being tired and sore; the screams and desperate pleas of the damned echo in the background.
It is Dean who draws these screams now, his knife cutting into a soul as Castiel approaches. He's too late; the Righteous Man has already given in. But still he approaches, intent on fulfilling his purpose.
The first time Castiel sees Dean his soul is tainted and already stained with the blood he's spilled. And yet there is still a spark of light inside him; something that this place hasn't managed to extinguish or burn away.
He doesn't understand as Castiel approaches, doesn't understand as he drags him up and out of the hellfire. He doesn't understand what makes him different, he can't see the light and potential still hidden inside.
The first time Castiel sees Dean he sees him not as a monster, but a man.
Basically this was an attempt to cure writer's block. I can't promise regular updates, or updates at all, but I'll try my best.