I can't believe I haven't commented on this since I absolutely love Fortress.

I like how you describe this from Dean's point of view: how hard it is for him to keep Sam quiet and undamaged, but how important it is to him to do it (and not because of Sam's place as a Pawn to Destiny, either). There's a real cold edge to Dean in these stories because, well, demon but he tries to remember what it was like to be kind. It's a fascinating balance. =]