Went to several interviews over a two and a half month period only to be rejected, with no feedback. Rakuten does not respect candidates or their time, there is no reason to stretch out so many interviews over such a long period of time. If you are unable to determine whether a candidate is suitable after two interviews the process generally doesn't work. I understand that some candidates will just not work out for certain jobs and I have no problems facing rejection, it's the waste of time that hurts.
As other reviews have mentioned expect a few months of waiting and multiple interviews rehashing the same questions over and over, with a new set of people. The interview process is also not set to eliminate people early on, as is the case in say the USA, so it's possible that you'll get rejected as I did after a few months of getting strung along. This seems to depend on the team for which you are applying, but the recent trend appears to be 4+ interviews each one getting progressively more difficult so be mindful of that.
My overall opinion of Rakuten is that they are very similar to RIM before the company blew up and essentially bankrupted. There's way too many managers, way too much red tape, and the ideals and values that they claim to favor are not given any actual priority in the hiring process. I was shocked that Rakuten could spare 1+ hour of several managers time on several different occasions just to hold a hiring interview. This indicates that there's either too many of them, or they don't have a whole lot to do every day. Neither of the two are a good image for the company from an outside perspective.
An overall disappointment, and huge waste of time. I would strongly recommend that others who are in Japan on a short term visa not waste their time with Rakuten. Yes, they do value native English speakers, but so do other companies and if you can speak Basic Japanese you'll have plenty of other, better options.