Applications for the Kumamoto Castle Marathon are being accepted beginning July 30 (Thursday) and will close at 17:00 on Sept. 10 (Thursday):
http://www.kumamotojyo-marathon.jp/outline_en.php
Unfortunately, though the English side of the web site announces that “applications will be accepted on the internet,” no English interface is available to accept those applications. (Sigh) It seems that you need to go through the Japanese interface here:
http://www.kumamotojyo-marathon.jp/entry_start.php
For additional information in English, see this translation of a Shisei dayori announcement:
http://www.kumamoto-if.or.jp/topics/topics_detail.asp?PageID=5&ID=7969&pg=2&sort=0&LC=e