Learn a Japanese song!
This is way more important then any lesson planning you do before you arrive. Esid I used basically the intro lesson a girl at DC orientation showed me. Total fail and changed it at least 4 times before I felt it was engaging and interesting for students.
So instead of worrying about lesson plans just bring a lot of pictures and stuff from your country. That preparation takes about a day. But what about the rest of the days between now and Tokyo orientation!?!?
Learn a Japanese song and wow your coworkers at the inevitable karaoke party. There are plenty of places to find lyrics to songs using the Roman alphabet.
Since I am in Okinawa I recommend Mongol800’s chiisana koi no uta.
Anything by akb48 … They did a song called sugar rush for the wreck it Ralph movie.
AI has a great song called happiness. It was used for a coke commercial but still super catchy.
Cutie Honey is a song from an anime.
Your coworkers will be thrilled with your “native” singing of American pop songs but it will really knock their socks off if you sing a Japanese song.