If you're heading in to the hills from ogaki on your own i suggest the following options:
1. Ascent of nishi hodaka. Take cable car from Shin Hotaka and then a 45 min hike to the Nishi Ho hut. THe ascent to the summit takes about 3hrs if memory serves me correctly and is a good fun winter scramble. If you're keen you can proceed on past the summit following the ridge to the main hodaka summit. Not done this but i presume you'll need a rope and some pro in winter....
2. Ascent of Koma ga take (central alps) possible in a day using cable car again. The wall at the back of the cirque will be snowy to about 40-50', otherwise a very straightforward ascent.
3. Ascent of Ontake San from one of the ski grounds on the lower slopes.
There are many many options for winter climbing in japan. Refer to the hiking in Japan books for other options, all those routes can be done in winter too. Remember that Japanese mtns get a good dumping of snow and some of the trekking type routes will require snow shoes, especially as you move nearer the northern coast.
For Fuji in winter your best bet is an ascent on the north side via the kawaguchiko route - watch out for the wind, the last 50 m can also be v icey and is not a good place to test your self arrest technique!