If you are having a hard time linking turns on a groomed black diamond, deep powder is going to kick your ass. Riding powder is completely different from hardpack, you have to let go of the edge-to-edge deal and basically learn to surf. It's going to frustrate the hell out of you until you get it, because you will be trying to make hard consistent turns and end up falling over and over again and get stuck, have to dig yourself out, and then have a meltdown. I think you will find plenty of chair-access powder in Japan, I would see how you do on that before considering doing backcountry.
PowderHound and TreeNinja