On this page you can find links to some real estate companies that help foreigners who are new to Japan to find housing.
Note 1: When a non-Japanese person has been resident in Japan for less than six months, they are usually prohibited from opening Japanese bank accounts which prevents them, in many cases, from being able to rent an apartment and get a Japanese mobile plan. This “liminal” (i.e. transitional) state is very frustrating, and working with a real estate company that is experienced in working through these kinds of constraints can be helpful.
Note 2: I have not used any of these services and I am listing them here for the sole reason that I have been approached by foreign students and/or their parents with requests for this kind of information.