Before you start

A residence card (zairyū card) and a registered address at your Tokyo ward office
A My Number (individual number), issued after you register your address
For shakai hoken: an employer that enrols you; for NHI: proof you are not covered by an employer plan

Step-by-step

1
Register your address, get My Number
Within 14 days of moving in, file your move-in notification at your ward office. This activates your residency, triggers your My Number, and is the gateway to either insurance route. Bring your residence card and passport.
In personWho: All new residentsWithin 14 days of arrival/moveFree
2
Employees: let your employer enrol you in shakai hoken
If you have a full-time (or qualifying 20+ hours/week) job, your company enrols you in Employees' Health Insurance — you do not visit any office. Premiums are split roughly 50/50 with the employer and deducted from payroll; the Tokyo employee share is about 4.9% of standard monthly pay. Your insurance card (hokenshō) arrives via HR, and a dependent spouse/children can be added at no extra premium.
Via employerWho: Salaried employees and qualifying part-timersEffective from your start date; card in 1-3 weeks~4.9% of monthly salary (employee half), payroll-deducted
3
Non-employees: enrol in National Health Insurance at the ward
Freelancers, the self-employed, jobseekers and students must enrol in kokumin kenkō hoken at the ward office's NHI counter — ideally the same day you register your address. Premiums are income-based, billed by the ward, and payable by bank transfer or convenience store. Coverage is retroactive to when you became eligible, so delaying just stacks back-payments.
In personWho: Self-employed, unemployed, students, freelancersSame visit as address registrationIncome-based; commonly ~¥15,000-30,000/month, varies widely
4
See a doctor — pay 30% at the counter
There is no GP-gatekeeper system: walk into any clinic or hospital that suits your problem, present your insurance card (and ideally My Number), and pay 30% of the cost on the spot. Start at a local clinic for routine issues. Arrive at a large hospital (200+ beds) without a referral letter and you pay an extra non-insured 'selection' fee (senteiryōyōhi) of roughly ¥7,000-7,700.
In personWho: Any insured residentSame-day, walk-in common30% of treatment cost (ages 6-69)

Documents you’ll need

Residence card (zairyū card)
Health insurance card (hokenshō) or My Number Insurance Card — bring to every visit
My Number notification/card
Passport and proof of Tokyo address (for enrolment)

Things most newcomers don’t know

Shakai hoken is materially better than NHI beyond just splitting the premium.

It adds injury/sickness allowance (shōbyō teate) and maternity leave pay that NHI simply does not offer. Newcomers fixate on the 50% premium saving, but the income-replacement benefits are the bigger reason employees come out ahead.

Source: Japan Health Insurance Association (Kyōkai Kenpo)

Always start at a small clinic, not a big-name hospital, for first-time non-emergencies.

Walking into a 200+ bed hospital without a referral letter triggers a ¥7,000-7,700 non-insured 'selection fee' (senteiryōyōhi) that a clinic referral avoids entirely.

Source: MHLW senteiryōyōhi rule

Apply for a 'limit-amount certificate' (gendogaku tekiyō ninteisho) before a big procedure.

The high-cost medical cap (kōgaku ryōyōhi) normally reimburses you later, but with this certificate the hospital caps your counter payment up front so you never front the full amount.

Source: MHLW kōgaku ryōyōhi scheme

The 30% co-pay does not cover everything — normal childbirth, most dental cosmetics and elective items are excluded.

People assume universal insurance means everything is 70% covered; routine pregnancy is handled instead via a separate lump-sum childbirth grant, not the 30% rule.

Source: Japan Living Guide; Kyōkai Kenpo

Common mistakes to avoid

Enrolment is NOT optional — every resident staying 3+ months must join a public plan; skipping NHI just accrues back-premiums you must pay when you finally enrol.
If you quit or change jobs, you fall out of shakai hoken immediately — go to your ward within 14 days to join NHI or risk an uninsured gap and retroactive bills.
Carry your insurance card to every visit; without it you pay 100% up front and must claim the 70% back later with paperwork.
#7119 is for advice, not dispatch — in a genuine emergency dial 119 directly; the ambulance is free but treatment still carries your 30% co-pay.