My first and only experience with the Koshu grape:
2004 Grace Wine Koshu Cuvee Denis Dubourdieu, Katsunuma, Japan, usually US$18, but I got it on sale for $8.
Very pale color and very light-bodied (only 10% alcohol). Subtle--anyone who expects a wine to beat him/her over the head with flavor will be disappointed. I found it to be a bit like a very mild Sauvignon Blanc enhanced by an intriguing jasmine aroma. It showed at its best with only a slight chill to enhance the aromas and flavors and to prevent the acidity from dominating.