The Foreign Earned Income Exclusion applies only to earned income, which your retirement funds are not.
So your only option is to go for the Foreign Tax Credit, where you can take a credit for taxes paid to Japan on income that you also paid tax on in the US.
Do a Search (upper right) for foreign tax credit and click on the jump-to link (Mac users must find foreign tax credit in the Topics List). NOTE: just type foreign tax credit and hit Enter; ignore any and all suggested Search terms.
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