Congrats on that you got the interview opportunity.
Even if you don’t get the position, you won’t lose anything and learn from the interview instead. So why to be so tense?
The only suggestion is very simple and not technical. Slightly rethinking about why you are interested in company in Japan? what you expected to get during this internship? what skills you have for this position? and what’s your ideal career path?
Please keep the following sentence in your mind. Being kind, optimistic and honest to answer all questions in the interview.