Not so quick answer - probably...

I've run into hotels which do not support a POLARIZED two flat blade plug. If the blades are equal width it'll work, but with a polarized two prong plug one blade will be slightly larger than the other & it won't fit into a non-polarized socket.

And you probably already know but Japan runs on 100VAC not 120VAC...generally the eastern part of the country like Tokyo is 50 Hz and the west like Osaka is 60 Hz. Almost all modern adapters will work great but do check the label to be sure.