This is a niche most guides get wrong, because the "obvious" Japan advice — "just open a NISA, it's tax-free!" — is often terrible advice specifically for Americans. Mio doesn't do vibes. Here's what actually applies when the US tax system follows you across the ocean. This is general information, not tax or investment advice.
Under FATCA, foreign financial institutions report US persons' accounts to the IRS. That reporting and compliance burden is why many banks and brokers around the world — Japan included — simply decline to onboard US customers rather than deal with it. In practice, coverage is uneven: some brokers refuse US persons entirely, some allow only Japanese-listed stocks (not US-based ETFs), and a few allow broader access. Because policies change and vary by firm, confirm current rules directly with the broker before assuming you're eligible.
The knock-on effect: NISA and iDeCo — Japan's tax-advantaged wrappers — are frequently inaccessible to US persons through a Japanese broker, or accessible only in a form that doesn't help you (see the next two sections).
Here's the trap. A non-US pooled fund — a Japanese mutual fund, investment trust, or ETF — is generally treated by the IRS as a PFIC (Passive Foreign Investment Company). For a US person, PFICs carry a punitive default tax regime and a notoriously heavy filing requirement: Form 8621, generally one per fund. Hold several Japanese funds and the paperwork alone can be crushing.
So the seemingly smart move — "buy a cheap Japanese index fund inside a tax-free NISA" — can be one of the worst things a US person does, because it combines a non-recognized wrapper with a PFIC. This is the single biggest reason to talk to a specialist before you buy anything.
The US taxes its citizens and green-card holders on worldwide income, no matter where you live. Living in Japan doesn't switch that off. On top of income tax, two reporting regimes commonly catch Americans abroad:
| Report | Rough trigger (verify current figures) |
|---|---|
| FBAR (FinCEN Form 114) | Aggregate value of foreign financial accounts over $10,000 at any point in the year |
| Form 8938 (FATCA) | Living abroad & single: specified foreign assets over $200,000 at year-end (or $300,000 at any time) — higher for joint filers |
| Form 8621 (PFIC) | Generally required per PFIC you hold — the reason foreign funds are so painful |
Thresholds and rules change and depend on filing status and residence — treat the figures above as illustrative and confirm the current numbers on the official IRS pages linked below.
None of this means Americans in Japan can't invest. It means the sane route usually looks different from what your Japanese coworker does:
1. Keep it US-domiciled. Investing through a US-based brokerage keeps your holdings inside the US tax system you already have to file in — and US-domiciled funds are not PFICs. (Separately, some US brokers restrict accounts for non-US-resident clients, so confirm your broker supports a Japan address.)
2. Prefer individual stocks over foreign funds. Owning individual shares avoids the PFIC problem that pooled foreign funds create. This is a tax-mechanics point, not a recommendation to stock-pick — diversification and suitability still matter.
3. Get a cross-border specialist. The US–Japan overlap (PFIC, foreign tax credits, the tax treaty, NISA/iDeCo treatment) is genuinely complex and high-stakes. A one-time consult with someone who does US–Japan returns can pay for itself many times over.
This applies to US citizens and green-card holders living in Japan — and, importantly, to "accidental Americans": people who are US citizens by birth or parentage but have never really lived in the US. US tax and reporting obligations follow citizenship and green-card status, not where you grew up. If any of that describes you, assume these rules apply and verify your situation.
Before you open any Japanese investment account, find out whether you're even eligible as a US person, and never buy a Japanese fund/ETF without checking the PFIC angle first. The default American-in-Japan playbook is: invest US-domiciled, favor individual stocks over foreign funds, keep filing FBAR/8938, and pay a cross-border specialist to sanity-check it. Next: NISA & iDeCo for foreign residents and the full arrival checklist.