Anyone who has watched the anime Kuroshitsuji has heard this sound as such "background music." It's a woman singing a few words I think, but I bet it's a part of a song and I want to know where I could find it and the name of it of course. It's played periodically throughout the series, at which point I don't know what episode it starts, just that it was earlier. The most notable time I remember it is towards the end moments of the last episode (episode 24). It's not in the soundtrack you buy off of amazon and whatnot (only like the OP and endings are included). I've been looking for it for awhile and it's FRUSTRATING <_<

If anyone can help me out, I'd be most appreciative. Thank you for listening.