See /usr/X11R6/share/doc/ja/rxvt/README.ja for more information
about using Japanese XIM.
If you want to enjoy menuBar features, add following 2 line
Rxvt*path: /usr/X11R6/lib/X11/rxvt/
Rxvt*menu: ja
to your ~/.Xdefaults.
Documents are at /usr/X11R6/share/doc/ja/rxvt/.