Before you start

Residence card with the address printed on it
A Japanese bank account or credit card, for most postpaid plans
An unlocked or eSIM-capable handset supporting Japanese bands
A Kobe address, for fibre

Step-by-step

1
Bridge the first fortnight with a travel eSIM
A data-only eSIM bought before you fly covers you until the residence card and bank account exist, which takes about two weeks. It removes the pressure to sign something unsuitable in week one.
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2
Go to an MVNO or a carrier sub-brand
IIJmio, mineo — which began as a Kansai operator — and the carriers' own low-cost brands run on the majors' networks at a fraction of the price with no long commitment. Flagship plans only make sense for bundled services you specifically want.
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3
Expect a Japanese payment method to be mandatory
Most postpaid plans need a Japanese bank account for direct debit or a Japanese-issued credit card, and foreign cards are frequently refused. This is why the bank account comes before the phone in every Japanese relocation sequence.
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4
Leave emergency alerts switched on and learn the 171 dial
Every Japanese network pushes Area Mail earthquake and evacuation alerts to handsets automatically, in Japanese and increasingly in English. NTT's 171 disaster message dial and each carrier's message board let people leave and retrieve voice or text messages when calls will not connect. Agree with your household now which of these you will use.
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5
Ask what actually reaches the flat before signing the lease
A building advertised as fibre-connected may run fibre to the basement and VDSL over copper to each door. Kobe's older hillside blocks and the 1970s and 1980s stock along the Hanshin corridor are particularly prone to it. Ask specifically about fibre to the room.
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6
Keep your number when you switch
Japan runs mobile number portability and has simplified it, so you can move between many operators without obtaining a transfer code first. Never cancel the old contract before the switch has completed.
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Documents you’ll need

Residence card with address
Japanese bank account or credit card
Passport, occasionally requested
Proof of address, for fibre installation

Things most newcomers don’t know

The 171 disaster message service exists because of what happened here.

In January 1995 the phone network across this region was overwhelmed within minutes — not primarily by damage but by everyone in Japan calling in at once, which locked out the people who actually needed to make a call. NTT's 171 dial and the carriers' web message boards were built so households can leave and retrieve messages without competing for a voice circuit. Agree a plan with your family before you need one; it is a thirty-second conversation.

Source: Ministry of Internal Affairs and Communications

The bank account gates the phone, not the other way round.

Most Japanese postpaid plans require a Japanese bank account or a Japanese-issued credit card, and foreign cards are commonly refused outright. Because the bank account requires ward registration and ward registration requires an address, the chain runs address, ward office, bank, phone. Attempting it in any other order produces most of the frustration people report from their first fortnight in Japan.

Source: community-reported

MVNOs run on the same towers for a fraction of the price.

Government pressure on the three major carriers produced both low-cost sub-brands and a healthy MVNO market, all riding the majors' own networks. Coverage and speed are essentially identical outside peak congestion. Anyone paying a flagship price without needing the bundled extras is spending several times more than necessary for the same service — and mineo, one of the better-known MVNOs, is itself a Kansai operator.

Source: Ministry of Internal Affairs and Communications

Japan's 100-volt mains and the 60 Hz western grid catch people with appliances.

Japan runs the lowest mains voltage in the world, so European appliances need a transformer regardless of the plug. On top of that the country is split between a 50 Hz east including Tokyo and Hokkaido and a 60 Hz west covering Kobe, Osaka and Nagoya. Chargers and laptops are fine either way; anything with a motor, a heating element or a timer bought second-hand from someone relocating from Tokyo may not be.

Source: community-reported

Common mistakes to avoid

Trying to arrange a phone contract before ward registration and a bank account exist.
Turning off emergency alerts because the first one woke you up.
Paying a flagship carrier price when an MVNO on the same network costs a fraction.
Assuming a building's advertised fibre reaches your flat rather than its basement.
Buying a 50 Hz appliance second-hand from someone relocating from Tokyo.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.