Apnea, you can already try to befriend a possible supervisor in a university if you want to. It will most likely be considered as an argument in your favor if you already have a place or multiple places to go, if you were to receive the scholarship.
However, you should keep in mind that a lot of professors in Japan prefer to wait until you get the scholarship, before they give you their support.
I would recommend you to try and get some contacts in Japan beforehand, because the period in which you have to select your Universities of preference, is rather short (and is also a holiday period for professors). You can try to find some Japanese professors who are researching in the same field of expertise and send them an e-mail.
This e-mail would include who you are, what you are studying now, that you will apply for the monbusho scholarship, a short summary of your proposed field of study (10 lines) and the question if the professor would be willing to read a full proposal (about 1 page) so that he or she can decide whether he or she would like to become your supervisor in case you got the scholarship.
I would recommend that you wait a little while longer to send out those e-mails. It is not even 2010 yet.Maybe in February or March would be a good time.
These are just mere suggestions of how I would do it, feel free to go your own way or listen to the suggestions of other people.