Song is "Rain" by Patty Griffin. Clips are from Tsubasa: Tokyo Revelations.
I really love the mood of this song. It's pretty and it's longing and I think it fits the somber moods both men go through when Fai becomes a vampire; although this AMV is mostly from Kurogane's POV, which I rarely see for KuroFai AMVs. Plus the rain is fitting due to the acid rain on top of things in Tokyo.
Disclaimer: I do not own any rights to the song, anime, and series used in this video. This is purely for fanmade purposes and entertainment. I make no profit from this.