Probably my favorite song that I have listened to. It's amazing how she is able to tell the story within her music. This song is just brilliant, and never gets old. As a whole Wolf's Rain Soundtrack leaps bounds beyond many other anime OST. And its all thanks to Yoko Kanno's genius. A masterpiece is the only way to explain something of this magnitude.
I think that "The most beautiful piece of music Yoko Kanno has ever written", mmm... I don't know, it's very difficult to say that, Kanno has a lot of styles. For example, have you listened to "TALLY HO!" from "Macross F"... is just powerful. Or "Power of the Light" from "Brain Powered", IS PERFECT. Or "Kuro no Keiyakusha" in "Darker than Black", AWESOME, or... "Bad Dogs no Biscuits" from "Cowboy Bebop".
Althought, anyway, this is a REALLY masterpiece. Beautiful melody. Kanno is a genius.