On receiving Japanese Pension overseas:
It is possible to apply from overseas, but it is probably easier to apply before you leave, if you have not already done so, or have your representative in Japan do it for you with a Power Of Attourney - 委任状
https://www.nenkin.go.jp/service/jukyu/ ... 40306.html
You can get paid to a bank account overseas, or to a bank account in Japan, but these days they force you to close Japanese Bank accounts when you leave, or at best limit access and available transactions if you plan to return, so that may not be a viable alternative.
You can fill out the Form,"Application Form For International Tax Convention" - 租税条約に関する届出書
https://www.nenkin.go.jp/service/jukyu/ ... les/02.pdf
"Application Form For Limitation On Benefits Article (US)" - 特典条項に関する付表(様式17-米)
https://www.nenkin.go.jp/service/jukyu/ ... les/03.pdf
and provide Form 6166 from the Internal Revenue Service
to receive permission from the National Tax Agency for payment of the Japanese Pension Gross, free of Japanese Withholding Tax.
https://www.nenkin.go.jp/service/jukyu/ ... hutsu.html
Under the US-Japan Tax Treaty Article 17
https://www.mof.go.jp/tax_policy/summar ... _ST_en.pdf
"ARTICLE 17
1. Subject to the provisions of paragraph 2 of Article 18, pensions and other similar remuneration, including social security payments, beneficially owned by a resident of a Contracting State shall be taxable only in that Contracting State.
2. Annuities derived and beneficially owned by an individual who is a resident of a Contracting State shall be taxable only in that Contracting State. The term “annuities” as used in this paragraph means a stated sum paid periodically at stated times during the life of the individual, or during a specified or ascertainable period of time, under an obligation to make the payments in return for adequate and full consideration (other than services rendered)."
Your Japanese Pension will only be taxable in the US, and not taxable in Japan, if you are living in the US.
(This is not the same if you are living in Japan, as the US reserves the right tax it citizens globally, despite the contents of Article 17... See Article 1...)