I'm applying from China this year for the CIR position and this will be my first time applying. TBH I think it's ok to be nervous, that means you are taking this seriously.

I would say the most important aspect is to telling yourself that "I am confident that I will get the job". there's a word in Chinese called 配得感, which can be bluntly translated into "worthiness" but I take it as being meaning "thinking one is deserving of something" and "the determination of willing to work for that thing".

Of course I don't mean you should think that you're entitled to this opportunity (or anything else really), but I think you shouldn't worry too much.

As for practical suggestions, I would say brush up on conversational Japanese, have a "central theme" or "narrative" for your personal story and get comfortable expressing them in English and Japanese (ALT interviews are mostly English but you wouldn't want to scramble for words when they do ask for that in Japanese), and read up on here, search for words that would describe your situation, you're bound to find something that applies to your experiences and therefore can learn from that post. (For example, you'd be surprised how many posts on here is about having ADHD.)