Looking at other reports here they seem to have a standard processes:
1. Video interview (record your answer to 5 standard questions on their Wepow platform)
2. 1st interview with the team members
3. 2nd interview with the team lead/manager
4. 3rd and final interview with supervisor of the team lead/manager
Step 2-4 were conducted via Skype as I do not reside in Japan. We used English during the entire process (email communication, Skype interview). Considering it is a Japanese company, the level of English spoken was surprisingly good.
It was not a difficult interview process for me, probably because I have extended experience in the area where they are lacking. There were very limited behavioral questions that you can easily answer, if you make some preparation. Before the final interview you need to read two books written by Hiroshi Mikitani and write on each a short essay. I'm not sure how important the essays are in the process, as nobody asked about them in the interview.
The process was professionally organized by the HR persons. The persons who interviewed me were also quite nice.
Although in the final interview it was indicated that I would get an offer, it didn't materialize. All in all it was a positive experience.