I added in this area more islands as well as you can see, such as Goto, Iki and Tsushima. But I also added more political instead of regional areas such as Tane south of Satsuma, and Awaji East of Kaido.
Here you can see the current capital of Japan in 1066. I added various landmarks such as lake Bima and completed the San circuits.
Here you can see the very populous Kyoto Region with some very powerful and influential provinces.
Mount Fuji in all its glory.
The less populated Ainu lands to the north(east).
As you can see the Ainu lands are currently split, and could potentially provide a powerful early rival for Japan if they manage to unite.
The Frozen wastes north of the Ainu provide an easy target to expand for an Ambitious Ainu warlord, or perhaps could even prove worthy of invading the South. (Props to anyone who conquers from the tip of Kamchatka.)