Even though java is supposed to have good cross-platform support and super awesome in every way, OpenJDK in Fedora 13 does not support Japanese fonts out of the box. It was pretty easy to fix. All you have to do is install the sazanami fonts and save this file as /usr/lib/jvm/jre/lib/fontconfig.Fedora.properties. Below is a screenshot of CGoBan3 with kanji working.
This seems to just be a case of an old config not updated, nothing more. So hopefully this will be fixed soon.