Google translate on an android phone is supposed to be able to translate Japanese writing to English. You may have to mess around some with different lighting to get enough contrast for the translator to make out the characters.
How is it currently wired?
Does it just have wires or are there terminals to connect to?
A pic of the inside of the box would be most helpful here.
Are the wires or terminals marked with those Japanese characters? since the rest of the plate is in English?
You know that the 2 outside wires are line and neutral
.
If the other two are connected together than you know it is wired for 220.
If there are 2 jumpers then it is already wired for 100.
It looks like this motor is clockwise only so you are good there.
If it is wired for 220 then remove the jumper, and your ohm meter will tell you which terminals are the ends of one winding. For 100V the windings are connected in parallel and for 220 the windings are in series.
Pay attention to motor heat, it is a 100V motor that you will be feeding 120. That is a 20% increace over design voltage. Where I work we have different windings for 100 V vs 120V. a 100V motor will run hot on 120,