How about a workaround?
I have a second VOIP line attached to my UK phone, it has a US phone number. Any calls to that number ring on my phone so I still receive calls from the US wherever I am, and they are local US calls (to US callers). I would suggest that you use a Japanese phone and a US 2nd number.
I use a service provider called TalkAtOne, (US based) and I am sure that others exist. Their rates are very low and the lines while a bit variable are average to good mostly.
It also runs nicely on an iPad, which I have discovered can become a handy desk speakerphone in a pinch.
Google also offer a free service (Google Voice) but it was absurdly complex to use.