Before you start

A residence card (zairyū card) issued on arrival, or in transit if applying with a foreigner-focused provider that ships before you land
A registered Japanese address for postpaid contracts with the big carriers
A payment method: a foreign credit/debit card or PayPal works with Mobal/Sakura/GTN; the big carriers effectively need a Japanese bank account or Japanese credit card
An unlocked phone, or buy a handset with the plan

Step-by-step

1
Decide: foreigner-friendly provider now, or big carrier later
If you have just landed (no Japanese bank account or credit card yet), choose a foreigner-focused provider: Mobal, Sakura Mobile or GTN Mobile. All three give you a genuine Japanese number, offer English support, and accept foreign payment. If you already have a Japanese bank account/credit card and read some Japanese, a big-carrier sub-brand (ahamo/povo/LINEMO) or an MVNO (IIJmio/mineo) is cheaper.
OnlineWho: YouSame day, or plan ahead before arrival
2
Order the SIM or eSIM and upload your ID
Sign up online. Japanese law requires identity verification, so you upload your residence card (and sometimes passport) before activation. Mobal and Sakura can ship worldwide or to a Japanese address, or you can collect at an airport/city counter; GTN can approve and ship same-day if documents are in order. Pick a physical SIM or an eSIM (eSIM activates fastest).
OnlineWho: YouSame day (eSIM/counter) to 1-2 weeks (overseas shipping)Setup fee around ¥3,300-3,960 with Mobal; varies by provider
3
Choose how you pay
Mobal and Sakura Mobile bill a foreign credit/debit card (Mobal also takes PayPal), so no Japanese bank needed. GTN Mobile is the standout if you have neither a Japanese card nor a bank account: it lets you pay by convenience-store cash. The big carriers and most MVNOs require a Japanese bank account or Japanese credit card for monthly direct debit.
Mobile appWho: YouImmediate
4
Later: port your number (MNP) to a cheaper plan
Once you have a Japanese bank account or credit card (usually after a few months), move to a cheaper sub-brand or MVNO and keep your number. Japan's MNP One-Stop system (since 2023) lets you apply directly to the new carrier online and authorise the switch in one flow. If your provider isn't on One-Stop, request an MNP reservation number (valid 15 days) and give it to the new carrier.
OnlineWho: YouOften after 3-6 months, once banking is set up

Documents you’ll need

Residence card (zairyū card) — the key identity/visa document for any contract
Passport (often required alongside the residence card for verification)
Payment method: foreign credit/debit card or PayPal (Mobal/Sakura), or Japanese bank account / Japanese credit card (big carriers and most MVNOs)
Japanese address for big-carrier postpaid contracts; not always required by foreigner-focused providers

Things most newcomers don’t know

The real barrier is not the residence card, it is the Japanese payment method.

The big carriers overwhelmingly want a Japanese bank account or Japanese-issued credit card for direct debit and quietly reject foreign cards, which a brand-new arrival doesn't yet have. You can have a perfect residence card and still be unable to sign a big-carrier contract on day one.

Source: Japan Living Life — best plans for foreigners

GTN Mobile lets you start a contract with NO Japanese bank account and NO credit card by paying at a convenience store.

For someone in their first week, before any bank account exists, convenience-store cash payment removes the chicken-and-egg problem entirely; most other carriers cannot do this, and it supports many languages.

Source: GTN Mobile — paying bills

The smart playbook is two-step: get connected immediately with Mobal/Sakura/GTN, then MNP-port to a cheap sub-brand once your bank account is open.

You stay reachable from day one with a real Japanese number, then cut your bill roughly in half later without losing the number employers, banks and apps already have on file.

Source: Smiles Connect — MNP One-Stop guide

Cheap data-only tourist SIMs give you NO Japanese phone number, so they can't receive the SMS codes banks and apps require.

Newcomers grab a tourist data SIM to save money, then discover they can't open a bank account or verify a PayPay app because there's no number to text. A voice SIM with an 070/080/090 number is what you actually need.

Source: Japan Dev — Japan SIM cards

Common mistakes to avoid

Assuming your foreign credit card will work with Docomo/au/SoftBank — it usually will not; they expect Japanese direct debit, which strands new arrivals.
Buying a data-only tourist SIM and only later realising it has no phone number, so you can't receive bank/app SMS verification codes.
Walking into a big-carrier shop in your first week without a Japanese bank account or address and being turned away.
Using a carrier-locked handset, which limits switching; buy a SIM-free (unlocked) phone or unlock yours before porting out via MNP.