this response is a tad late, however, here goes...
I studied (4 wks, then returned for another 2 wks) at Yamasa institute in Okazaki, Aichi-ken (near Nagoya). It was brilliant - even has its own little bar on campus, for a nice weekend thirst quencher. Teachers were very patient, helpful & encouraging. Great student support & good accommodation close to school. There is a good variety of course types & short duration is no problem -see their website. www.yamasa.org/
Okazaki is a great place if you love Japanese history & also it is easy to travel to kyoto, Nara, Tokyo (~ 2 hrs by shinkansen). I wish that i could have stayed longer.
Enjoy -wherever you go.