Because I legit just spent ten minutes typing variations of "harry potter + supernatural + buffy + dean/hermione + ginny + faith + new york" into google in hopes of rediscovering this particular story. None the less, it is quite possibly the shortest time it has ever taken me to find a Fic Lost To Time And Faulty Memory. Archive Of Our Own rocks, yo.
Cracked Stars Shining by abi z (azephirin). It has, quite possibly, been almost a decade or more since I first discovered this story. It may say 2009 on the publish date, but I'm pretty sure I first discovered it when Live Journal was in it's hey day back in the mid 2000s, but it never made it into my fic recs because the story was never completed. It still appears to be incomplete, but if I am recalling correctly, it also doesn't end in a particularly cliff-hangery ending, which is always a plus. I also don't remember much else that happens in the story, really, beyond some Dean and Hermione making a surprisingly awesome couple, Faith being mildly obsessed with ICanHasCheezeburger, Hermione chopping off all her hair, and some PSTD/sexual assault type things for Ginny (so TRIGGER WARNING; they are only mentioned in passing, but still... not fun) that Sam slowly but surely helps her work through in the background. Still, though, it stuck with me all these years and it will definitely be getting a reread in the not so distant future.