Congrats to those who've had confirmation and good luck to those waiting, like me!
I've had my interview last week and since so many people are sharing their experience, I might as well share mine too. Also, first things first: thank you Flidar for those questions, they really helped me prepare for the interview because they handled subjects I didn't think of myself

So, my interview was supposed to take place at 11.20 but they were running late by almost half an hour. I was really nervous, but it also helped because I could ask other people about their interviews and their research subjects. When it was finally my turn, I entered with a "shitsureishimasu" and "ohayougozaimasu" (and left with "shitsureishimashita") because I knew who would be sitting in the room and I knew it'd make a good impression. The panel consisted of my Japanese professor, a Japanese professor from the only other university in my country that teaches Japanese, a respresentative of the Japanese government and a respresentative of my own government.
The interview started with the Japanese person, who introduced everyone and asked me some things about myself and what I would like to research. He also asked why I didn't apply for a doctoral course (I applied for Research Student) and what I was planning to do with the results, all in English. Then the prof of the other univ asked me some things in Japanese about the thesis I wrote last year, because he knew a bit about the subject and he tried to test me whether I still knew what I wrote and if he could confuse me with asking direct questions in Japanese. (Last year I horribly failed at this guy's questions D: ) But this year I knew what to expect and I even made the guy laugh (which is a good sign, from what I've heard).
After that was my own professor, and I didn't expect him to go easy on me, which he didn't (he did, however, ask me everything in English). He's a great professor and he expects the best out of his students, and from his actions I believe he was pleased with me (I think)... He asked me some details I failed to mention in my research proposal, such as a rough time schedule, how I was going to conduct my research and what kind of group of people I'd research (things I luckily prepared in advance!

). This was probably to allow me to fill in some important gaps I left in my documents. The guy from my government didn't ask anything, since he couldn't understand Japanese and basically he's just there for show XD
Other questions they asked:
-why did you contact this professor/choose this university/this subject,
-have you heard of any of the professors you contacted (luckily I had! This is always a good point!)
-if I had read this professor's publications and knew of other researchers who wrote about the same subject as mine
-why I didn't conduct my research here or in America
-why the publications that already exist about my subject aren't good enough
-...
so mostly stuff that has already been mentioned here. I have more confidence in this year's application than in last year's one, but with more than double the applicants, I have no idea what to expect... ☝