Where the rule actually comes from
Not from the bank. It comes from the Foreign Exchange and Foreign Trade Act (外為法) and the Ministry of Finance directive interpreting it — 蔵国第4672号, in force since 1980.
Under that directive a foreign national is treated as a non-resident (非居住者) by default. You become a resident (居住者) when either of these is true:
- Six months have passed since you entered Japan, or
- You work at an office in Japan (本邦内にある事務所に勤務する者).
These are alternatives, not conditions to satisfy together. If you work at a Japanese office you are a resident from the day you start — there is no six-month wait for you, and never was.
So who does have to wait?
People without Japanese employment. Students before they start work, dependants on a spouse's visa, and people who arrived on a long-stay visa but aren't employed here yet. For them the six months is real, because nothing else makes them a resident.
It also explains the thing that confuses everyone: two people arrive the same week, one opens an account immediately and the other is refused. They weren't treated inconsistently. One was employed.
What this means at the counter
- If you're employed, bring proof of employment — a certificate of employment (在職証明書) or your employee ID. It is what moves you across the line, and a branch that can't confirm it may default to treating you as a non-resident.
- Bring your residence card with the address already registered. Register your address at the city office first; the bank needs the card to show where you live.
- A Japanese phone number is generally expected, which is why getting a phone plan sorted tends to come first.
Why this matters beyond the account
The bank account is the gate for nearly everything else, and its absence is what makes the first months awkward. It's also why the credit card requirement on fibre internet bites so hard: a Japanese credit card needs a payment history, a payment history needs an account, and the account was the thing you were told to wait six months for.
If you're employed, that chain is shorter than you were told.
The residency rule above is from the Ministry of Finance directive and is quoted as written. Which documents an individual branch asks for varies, is not centrally published, and is marked checking until we can source it properly. Do not treat the document list as exhaustive.