Hello Scott,
I have been visiting Japan this September 2017 and some information about SOTA operation in Japan is shared in this thread:
Mela @JI1KBF was sharing infos about correct portable callsign usage in JA:
For the guest license if you are not using a radio with a Japanese ‘technical standard number’ (that’s somehow like a CE mark in Europe or FCC approval I guess) then you have to pay and extra assurance fee and send over that radios technical documentation for verification. You will then receive with you license documents stickers to put on the radio to show they are approved by authorities.
Regarding bands JA SOTA Manager Toru @JH0CJH was a great support and shared upfront by email a lot of facts:
2m FM not recommended during the week because of illegal operation by non hams (at least near big cities)
2m SSB is possible
Instead go for 70 cm:
SSB 430.190 to 430.250
FM 433.0 is the call channel and widely used from 432.5 to 433.5MHz
MHz in step 20kHz
On 50 MHz the following freq is widely used in Japan an popular for SOTA
SSB 50.160 to 50.250
AM 50.550 or 50.600
MHz in step 20kHz
In addition I was working 20m band and used the QRP typical 14.285 MHz.
20m and 30 m cannot be used by JA beginner class 17m can be used for beginner class in JA. Might be worth trying too (CW).
If you are using APRS for spotting/tracking:
144.640 MHz with 9600 baud is more common than 144.660MHz with 1200 baud
Be mindful setting alerts on sotawatch because of timezone rollover. It happened to me that I was alerting the wrong day 
73’s de Joe