In reply to Pete Houghton:
Hi Pete
There are only four routes on Fuji, and you can't really stray off them and pick your own line up in the summer, you'd be committing a major faux-pas as well as potentially knocking down a lot of rocks. There's no point in straying off the established trails anyway in summer, as the terrain is all pretty much the same. You'll find a lot of people on the trails through the July-August hiking season, and the most jammed times near the summit will be early morning when most people are heading up for sunrise. It's much more comfortable to leave it a bit later in the day and avoid all that stuff...
The longest route on the mountain is the Gotenba route on the eastern aspect. The 5th station trailhead on that side is at about 1400m, whereas the others are approx. 1000m higher, so Gotenba gives you a good 2300m of elevation gain.
This website will tell you what you need to know:
http://www.fujisan-climb.jp/en/access/#block2
As Lion Bakes mentioned, make sure you take the right trail down from the crater if descending in the dark, as by the time you get down to the 5th station on the wrong trail you'll be screwed, miles away from your car and no obvious way to get back there
The mountains up north (Iwate, Aomori etc.) will be snow free by the time you're there. There are lots of good mountains up there for hiking and trail running (Hakkoda-san, Iwate-san, Akita-komaga-take etc.). Shoot me a mail if you'd like any more info closer to the time of your trip.
Alternatively, if you'd prefer ideas for more technical climbing routes/areas in Japan, feel free to take a look at my site (
http://climbjapan.blogspot.jp/) or book (
http://amzn.to/1U6ydqx).
All the best!