There are plenty of guides on hiking mount Fuji, and how to get there in the summer (the "open" season, July- early September).
I have read and been told that although the routes are technically closed after mid-September, and highly advised against between November and June (due to snow and bad weather), they are still accessible/open "at your own risk." It's just that the huts/stations are closed, and the busses/trains don't run (so you need a car).
Has anyone had experience with this? Can you drive to the 5th station (of any of the routes)? Are the paths still open?