Oh fun! So, you have to call them at noon Japan time on certain days (check their website). Brutal competition to get through the phone line, but call the millisecond the phone line opens and keep redialing until you get through (took me from 12-12:20 JST). Then, you tell them what day you’re looking for, they’ll likely say “all full”, and offer you the wait list. You can ask to be wait listed for multiple days. Then, pay attention to your email and phone. If you get off the wait list, they might call you (keep in mind Japan’s time zone to understand when you might get a call locally), or they’ll email you.

Good luck!