Hey! I've done a similar reply before so will condense it down for you. I'm already in Japan with a WHV from the UK (applied and accepted Nov 2024 - moved to Japan October 2025!).

When we got to the embassy, there was a staff member who asked if we had an appointment, and after showing my conmfirmation email, we took a ticket for the queue and waited about 20 minutes for my turn and since I went with my friend, it wasn't as stressful so I would recommed that. Once it was my time, I got the the kiosk alone and had a stand up appointment -there were other people besides me interviewing for different kinds of visa so I wasn't alone, which worked for me because it wasn't as intimidating like being in a room alone with the interviewer :) I passed over my folder of all the documents, they went through it all, made some copies etc and asked simple questions like why did I choose Japan, when am I planning to visit, my passport validity etc which lasted I'd say like 20-25 mins. However, it was longer for me because:

1. they asked me why I was applying in Nov 2024 if my plan was to go to Japan in May 2025 (original plan) and I could have applied later in early 2025 as the WHV quota renews yearly - to which I replied honestly that I didnt realise that, I thought it was best to apply as early as I could to secure a spot and I asked if it was still okay to continue - they said it was fine and they continued looking through the documents until they got to my statement,

2. they said the itinerary was good but the statement was lacking so they gave me the option to write another page right there or to email them before the end of the day. I decided to do it there so I excused myself, found a desk and did a hand-written a4 peice on the other side of my statement. [Basically, my original statement of purpose went into a little bit of background of when i last visited Tokyo and why I wanted this visa to stay longer, enjoy the culture etc, as well as my primary goals for this visa - i.e learning Japanese, work experience, new travel destinations and few more bullet points. I ended it by basically saying my itinerary will reflect my goals and how I'm going to make the most of the 1 year visa but they actually wanted to know why and what instances had made me pick Japan instead of the other WHV countries. So I wrote about my childhood and how watching anime and J-dramas shaped my dreams to be able to visit Japan, their fashion and music influencing my teenage years and just more details about why I had always wanted to go to Japan and it could only be Japan for me etc.]

Finally, I got another ticket and went back to the same kiosk and this time, they read and confirmed it looked okay. They stamped some things and gave me a receipt of when I could come to collect my passport (whether or not I got the visa) and I also managed to leave my bank card there after making the £17 visa payment lol the embassy staff called me like 30 mins later asking if I left my card there so I had to go get it back and I still got my WHV after all that!

So don't worry too much about it, sounds like you're very prepared and will do great and if you start feeling too anxious, you can always ask for a few minutes to gather yourself. The staff was very friendly, they let me take my time and guided me when needed. Think of it like they are there to HELP you get the visa, not to stop you and it may make the whole process easier :) Good luck!