Well...
In terms of ID verification, I was able to provide my passport and drivers license to AU in their shop in Tokyo and it was OK.

The catch is that I was just trying to verify my ID so they didn't turn off my prepaid phone. The shop wanted a gaijin card! I explained that there was no way they were going to take a $200 from 2 years ago me for the phone and then turn it off. However, somehow she called HQ service center and they said it was possible.

If I walked in there with zero Japanese ability my phone would have been history.

Not sure about buying a new phone.

Regards,

Scho