James, good for you for studying in Japan.
It takes courage and a good sense of adventure to enter a dojo where you are the only foreigner. Eventually, though you will become less of a foreigner to the folks you practice with and almost like family.
Regarding books, assuming you are practicing Aikikai style Aikido and not Yoshinkan or Tomiki or Ki Society, the best bet is the two books written by the Doshu Moriteru Ueshiba. I say this because they are quite literally the translation of two books that were written in Japanese and can be found in most Aikikai Dojos in Japan (the Japanese version that is). The same picture sequences are in both books, so you can reasonably ask questions of your Sensei through the use of the book.
If you're not studying Aikikai Aikido, it's still a good book, just probably not the most important one for you to buy.....