Because you are a U.S. Citizen, I would advice you not to take the Form 8833 position. I know there may be other website claiming that a dual citizenship can use this form or other tax treaty forms.
Based on what the IRS publication, there is no such position that an US citizen with dual citizenship can reduce U.S. citizen liabilities.
The U.S. does not reduce its claim to its citizen because the person also holds another country's citizenship. That is not why the tax treaties are signed.
A reduced-tax treaty position in tax is usually to protect the citizens of each perspective country respectively.
Dual citizenship is allowed in many aspects of a person's life here and abroad. But there is really no IRS or tax position for naturalized citizens to be treated differently and more favorably than the general public in filing the U.S. tax return. For an U.S. citizen, the income is taxed on worldwide income.
We can say that a treaty has a higher authority than U.S. tax law. But the tax treaty also serves a different purpose.
If for the same income, you paid Japanese taxes, the U.S. income tax allows you to use foreign tax paid deduction on schedule A or foreign tax credit on Form 1040.
It is recommended that you take the position of a U.S. citizen when filing U.S. tax returns.
I am not sure you can or want to exclude social security benefit from your tax return. Taking such a position is similar to claim not qualify to receive social security benefit. It and other income may be U.S. based income.
"Generally, you must file a return if your gross income from worldwide sources is at least the amount shown for your filing status in the Filing Requirements table in Chapter 1 of Publication 54, Tax Guide for U.S. Citizens and Resident Aliens Abroad." (Bold and underline added.)
Fiona Chen, MPA, Ph.D., CPA, ABV, CFF, CITP