As it happens, I'm writing a similar one-shot at the moment. My Regulus quite literally drunk the potion about half an hour ago.
But on with the review.
Holy literary references, Batman. :P
The Dark Mark being Regulus' mark of Cain is a really interesting viewpoint/analogy/thing. I don't quite characterise him like that myself (sorry, I'm stuck in between-fits-of-writing mode) but it totally makes sense, although I'm not sure how acquainted he would be with Biblical stories.
Thing is with stream-of-consciousness-y writing - at least, in my opinion - is that it's hard to separate the third-person narrative voice from the voice of the character, and so it feels a bit like you're expecting me to believe the not-rebellious son of a pureblood anti-Muggle family is going to reference Shakespeare/the Bible/Muggle mythology and history/etc. I don't know if that made sense or not, or if I'm reading it wrong, so sorry about that.
Apart from that probably-misguided quibble (that's the first time I've ever used that word!) Your Regulus is strangely adorable - he's quite childish with his fantasies and his love for Sirius, and juxtaposed with the darkness of his situation and his more detached thoughts, it's very effective. He seems to be so utterly removed from everything except his situation, which is understandable given its nature I guess, and you've shown that very well.
Speaking of separation: I also very much liked how you've got both Sirius and Voldemort as absences rather than presences - or at least, that's what it felt like to me because we don't see either of them - because it just... I don't know... creates another sort of barrier between Regulus and the rest of the real world. And considering the prompt for this fic, that's a very good thing.
And now I have run out of things to say. Hrm. It didn't feel unfinished to me, and I'm not sure how you could really make a satisfactory-to-you ending... him being dragged underwater by Inferi might've broken the mood a bit.
Anyway. This was unbelievably fantastic. And I'm sorry about this terrible review.
Author's Response: I'm very sorry for not responding to this sooner. It's a fantastic review, one that's left me with a lot to think about, and those are the kind of reviews that I like best. Perhaps I've put it off because I've been savouring it for too long. Well, and because when I had this lovely detailed response written up, I accidentally exited the page and lost it. Now I'm trying to remember what I had written (and it's never as good when one tries to rewrite lost things).
Thank you very much for taking the time to read and review this story! It was exciting to receive a review from you, as your Marauder character studies are among the best I've found on the archive. I've been curious what you'd think of this version of Regulus, which, as you said, is childish and detached. It's not how I think of him normally, but it worked interestingly in the context of this story.
The part of your review that had me thinking the hardest was that regarding the Biblical reference. I have to admit that I didn't think about /how/ Regulus would know of that image - it was one that struck me as of particular interest, so I ran with it. I would have gotten away with it if not for the close narration, the stream-of-consciousness style (which in this story is more like free indirect discourse - it's not a true SOC). I can find an excuse for the Shakespeare, as in my headcanon, Shakespeare and other such individuals are wizards and witches who find success in the Muggle world. (There's really no better way of explaining why the Bronte sisters were so strange.) Plays like "Hamlet" and "Macbeth" seem like appropriate texts for the libraries of purebloods. But the Bible... I can only put it down to an unfortunate inconsistency in the story. It's something I will watch for when I try this style again - when I saw it in your review, I had to facepalm and shake my head in embarrassment that I'd missed something like that in my enthusiasm.
Yes! Your reading of Sirius and Voldemort as absent presences is exactly what I was going for! It is something that JKR makes some use of within the books, particularly with Lily, but I wanted to make Sirius and Voldemort echoes in Regulus's head. They are the most influential figures in his life, followed by his mother, and he hears their voices, knows exactly the kind of things they would say in reaction to the things he does. Regulus strongly desires to connect with them - with anyone in fact - but they betray him. So while his mind keeps going back to their words, they can never be fully present in his world. Regulus cuts himself off from the world that has neglected him, betrayed him, and that will forget him. Only Kreacher is left to care, and no matter how much affection and kindness Regulus shows him, Kreacher is always "just" a house elf.
Thank you again for this review! I'm still failing a little over it, even after two months.