A rained-out day in Tokyo is a problem you solve with your phone. You check how long the band of rain lasts, you find something indoors nearby, and you book a timed ticket for it — usually in that order, usually standing under an awning.
None of that works if you’re offline and hunting for station Wi-Fi. This guide is about making sure you’re not.
First: does your phone actually support eSIM?
Do this now, at home, not at the airport.
On an iPhone: open Settings → Cellular (or Mobile Service / Mobile Data, depending on your region’s wording). If you see an option to add an eSIM or convert to eSIM, you’re fine.
On Android: Settings → Network & internet → SIMs, and look for the option to add a SIM without a physical card. Wording varies by manufacturer more than it does on iPhone.
Two things that catch people out:
Carrier locks. A phone bought on contract from a home carrier may be locked to that carrier, and a locked phone will refuse a Japanese eSIM even though the hardware supports it. If you’re not certain, ask your carrier to confirm the phone is unlocked before you travel. This is the single most common reason a traveller’s eSIM plan doesn’t work, and it’s not fixable from Japan.
Model age. eSIM support has been standard on flagship phones for several years, but the details — including whether your phone can run two eSIMs at once, or an eSIM alongside a physical SIM — depend on the model. Apple documents this per model on its Dual SIM page (opens in a new tab), and it’s worth five minutes before you buy a plan rather than after.
When to buy: before you fly
You can buy on arrival — there are counters and vending machines at the major airports — but buying before you fly is better for three reasons, and none of them are about price.
You install it while you still have working internet. Installing an eSIM requires a connection. Doing it at home over your own Wi-Fi, with your own carrier as a fallback, is a completely different experience from doing it in an arrivals hall on a network you can’t reach.
You find out early if something’s wrong. A locked phone discovered three days before departure is an annoyance. Discovered at Narita, it’s your whole first day.
You’re connected the moment you land. Most plans let you install now and activate later, so you scan the code at home and switch it on when the wheels touch down.
How the plans are sold
Japan travel eSIMs are generally sold by duration and data allowance — typically blocks of 7, 14 or 30 days, with a fixed number of gigabytes, rather than genuinely unlimited service.
Two things to read before you pay:
- What happens when the data runs out. Some plans stop; some throttle to a slower speed. A throttled plan that still loads maps is far more useful on a rainy day than one that simply stops.
- Whether you get a Japanese phone number. Most travel data eSIMs are data-only. That’s fine for maps, messaging apps and booking sites, but it means you can’t receive an SMS code, and some Japanese booking systems want a phone number. If that matters to your plans, check before buying.
We’re not printing prices here. This is a market where plans and pricing change constantly, and any figure we published would be stale before your trip. Compare on the day you buy.
Where to buy
The straightforward route for most visitors is a marketplace listing, because you get English support, a card payment in your own currency, and a QR code by email within minutes. Klook’s Japan eSIM voucher (affiliate) (opens in a new tab) is the one we point people at: it’s a nationwide data plan, it shows current pricing and the data allowances before you pay, and the voucher arrives as a scannable QR code.
Buying direct from a Japanese carrier can work out cheaper on longer stays, but it usually assumes you can read Japanese and, in some cases, that you have a Japanese address. For a two-week trip, that trade isn’t worth it.
Whichever route you take, the checks in the next section matter more than the vendor you pick.
The setup sequence
- Buy the plan and receive your QR code — usually instantly, by email.
- Scan it while you’re still on Wi-Fi. On iPhone: Settings → Cellular → Add eSIM, then scan. Apple’s official walkthrough is linked above if the menu wording on your phone differs.
- Label it something obvious — “Japan” — so you can tell it from your home line at a glance.
- Choose which line does what. If you’re keeping your home SIM active for calls and texts, set the Japan eSIM as your data line and leave the home line for voice. Turn data roaming off on the home line so it can’t quietly run up charges.
- Test before you leave the airport. Load a map, not just a web page. If it works in arrivals, it’ll work in the rain.
When it goes wrong
The QR code won’t scan. Display it on a second screen — a laptop or a travel companion’s phone — rather than trying to scan a code on the same device. Most vendors will also resend it through their support chat.
Installed, but no signal. Toggle airplane mode on and off. Then check that the eSIM is actually selected as the active data line rather than just installed — this is the usual culprit.
It worked yesterday and doesn’t today. Check whether you’ve hit the data cap. Video and photo backup eat allowances far faster than maps do; turning off automatic photo upload for the trip is a good default.
Nothing works at all. Convenience stores, station buildings and most cafés have free Wi-Fi, which is enough to reach your vendor’s support chat. Have that as the fallback plan rather than the main plan.
What to point it at when it rains
The reason you did all this:
- JMA rainfall nowcast (opens in a new tab) — the Japan Meteorological Agency’s official short-range precipitation nowcast, available in English. This is the one to check before deciding whether to wait out a shower or commit to an indoor plan.
- JMA English portal (opens in a new tab) — forecasts and, more importantly, official warnings. In typhoon season this is the source that matters, not an app’s summary of it.
Both are government sources rather than aggregators, which is exactly what you want when the weather is the thing making your decisions.
The short version
- Check your phone is eSIM-capable and unlocked — before you fly.
- Buy and install at home — for example Klook’s Japan eSIM (affiliate) (opens in a new tab) — and activate on landing.
- Set the Japan line as data, home line as voice, roaming off.
- Test with a map before leaving the airport.
- Bookmark the JMA nowcast — it’s the reason you’re connected.
Part of our complete rainy-day Tokyo itinerary — the one thing to set up before the rest of the day begins.