As most people can relate: I remember so little of this story, but I remember I loved it!

Sam and Dean aren't related when the story starts (I can't recall if it's later revealed that they are in fact brothers or not).

I think the story started off with Dean busy skulking through a neighborhood looking for a werewolf (?).  He stumbles into Sam, who's also looking for the murder-villain-thing that's been killing people, idk.  They pair up and fight/kill it.

Sam's got an abusive father who beats him.  Dean offers to take Sam away with him when he leaves after the case, but Sam opts to stay.  I think Dean comes back for some reason to find Sam getting the snot kicked out of him, and so he spirits Sam away. La di da.

And I think from there they just kinda.... hunt and stuff (and sex), but Sam might still have visions or some connection to YED?  I don't recall if John was present in the story or not; if he was, I don't think he trusted Sam or he was cagey about Dean's dead baby brother.... I could be mixing stories here, though.  God, I can't remember and it makes me so mad >:C

I only remember the very beginning -- that they weren't related/didn't know they were related, and that Sam's dad abuses him.

I've been looking for this FOR MONTHS omg, if some one knows what it is, I will LOVE YOU 5EVA.

(Also -- No, I'm not looking for Ouroboros by thenyxie, nor am I looking for Samuel Winchester and the Death of Azazel the Deathless by Ninhursag -- though both are very, very, very good.)

FOUND!: Full Moon, Fast Cars Series ((Massive thanks to montana_highway!!))