VISIT JAPAN 21 MARCH - 21 APRIL 2016

Hi,

Since you are starting in Kansai, going south to Kyushu, and then upwards all the way to Sapporo, it should be relatively easy to get your money's worth in a 21 day pass. The logical course of action since you are staying one month and using a 21 day pass would be to start out in Kansai, see the area for a week or so until you are satisified, then activate the pass and go down to Kyushu, working your way northwards.
For your time in Kansai you might be able to use some regional passes for the area; see:

http://www.japan-guide.com/e/e2357.html

The good news though is that you will be in Japan during the cherry blossom season, and you can follow it as it spreads from south to north, usually starting in the main islands from the end of March.

Your question of using it as a regional pass is somewhat unclear. You can use it on JR routes and buses, plus the Miyajima ferry. You cannot use it on non-JR lines, city subways, etc. The pass is of limited use in Tokyo and Osaka (only on the JR loop lines), and for some areas like Hakone or the Fuji 5 Lakes area you'd need to buy a different company pass to see the area on a discount.

Everything else is up to how you want to allot your time and what you want to see.

Thank you Toraneko. That was my plan too to travel south. Noted and looking forward to my rail trip to Japan.