The idea of Dean giving the Mark of Cain to Sam (even if it's with the intention of saving his life/sparing him) is probably the most horrifying thing I've ever read in any fic I've read in any fandom (and do you have any idea how many tentacles were consistently and canonically involved in my two fandoms previous to this one?!)--and I think conceiving of that moment as part of, well, the trajectory of the Winchesters' lives and their relationship to/dealings with each other really augments that. I love the way the frenzy of the first part of this, its nonlinear jumps between tense moments, contrasts with the second part where Sam and Dean reunite at Sam's house (though the fic never once takes its foot off the gas, even in moments of relative calm). And I adore Castiel's final two paragraphs, as he watches the sun set on an ending that, if it must end (as it always does) in blood and fire, is "not really a bad thing after all." Gorgeous work as always, bb. <33333 I love this.