I think the main thing in japan is that you have to search out the steeps and sometimes you have to put up with a bit of a hike or be prepared for a quick escape from the patrol.
as far as the better steep/advanced sections i've found so far, i think the run from the peak to hanazono in niseko is the best - fast, steep and with some interesting trees at the end. the only drawbacks are the hike if you take the wrong line and the volumes of people on a good day.
apart from that:
hakuba 47 has some good stuff under the quad lift,
nozawa some fun but not so steep sections around the top