The Japanese tax benefit, the lack of automatic US exemption, fund-selection complications, broker restrictions, and reporting.
A US citizen resident in Japan can open NISA and it removes Japanese tax, but it gives no US exemption; the fund you hold inside can create PFIC and reporting problems, so NISA can still have value only after a careful, product-specific US analysis.
A US citizen or green-card holder who is a Japan resident can generally open NISA — eligibility is residence-based. Inside Japan, NISA works normally, removing Japanese tax on qualifying gains and dividends. The critical point is that NISA is a provision of Japanese law, not the US Internal Revenue Code, so it gives no US exemption: the US taxes citizens on worldwide income, and NISA income can still be US-reportable and taxable.
So a US person gets the Japanese benefit but keeps full US obligations. Whether NISA is worthwhile depends heavily on what you hold inside it and how the US treats that holding.
The complication lives in the holdings. A Japanese-domiciled mutual fund — the standard beginner choice inside NISA — can be a PFIC for US purposes, potentially requiring a separate Form 8621 per fund and punitive taxation or complex elections. So the "obvious" low-cost index fund can be exactly the wrong pick for a US person without analysis. Individual eligible stocks are generally not PFICs, and US-domiciled securities avoid the PFIC issue but raise their own broker-access questions.
Some brokers also restrict US persons: Rakuten, for example, states US persons may not trade its foreign-stock products, and others impose different rules. These are commercial/regulatory policies, not a universal NISA rule.
NISA can still be worthwhile for a US person, but only after a product-specific analysis. If you hold US-domiciled securities or individual eligible stocks that avoid the PFIC problem, NISA’s removal of Japanese tax may add genuine value with manageable US reporting. If you hold Japanese mutual funds without analysis, the US PFIC burden can outweigh the Japanese benefit.
The safe sequence is to complete cross-border advice before buying anything inside NISA, covering PFIC classification, Form 8621, FBAR, Form 8938, foreign tax credits, and estate exposure. NISA is not automatically good or bad for a US person — it depends entirely on the holdings and the reporting they trigger.
Brokerage (NISA/iDeCo) · Rakuten Securities
A leading low-cost brokerage for NISA and index-fund investing, integrated with Rakuten points and Rakuten Bank.
Fees: Many domestic funds and trades are low- or no-commission — verify current fee schedule.
Brokerage (NISA/iDeCo) · SBI Securities
Japan’s largest online brokerage by accounts, with a very broad low-cost fund lineup and full NISA/iDeCo support.
Fees: Many trades and funds are low- or no-commission — verify current fee schedule.
Brokerage (NISA/iDeCo) · Monex
An established online brokerage often chosen for US-stock access and research tools, with NISA and iDeCo support.
Fees: Commissions vary by product; some funds/trades are low-cost — verify current schedule.
Be very careful. Japanese mutual funds and ETFs are usually PFICs (Passive Foreign Investment Companies) for US tax, which triggers punitive US taxation and heavy Form 8621 reporting — and the NISA tax exemption does not apply to the US. Many US persons in Japan avoid Japanese pooled funds and instead hold US-domiciled assets, but rules are complex. Get advice from a cross-border US/Japan tax professional before investing.