eSIM for Japan

Japan is a country you navigate through a screen: platform numbers, station exit letters, restaurant waitlists and the time of the last train back are all things you look up rather than ask about. A Japan eSIM puts a local data line on your phone before you have cleared immigration at Narita, Haneda or Kansai, and it sits alongside your normal number instead of replacing it. Nothing gets swapped out at a counter, nothing small gets lost in a hotel room, and your first train is planned before you reach the platform.

Getting online when you land

Install the profile at home, on your own wifi, while you still have a working connection. The install step itself needs data, which is exactly what you will not have standing in the arrivals hall. Leave the line switched off until you get there.

When the wheels touch down, come off airplane mode, turn the travel line on, and set it as the line your phone uses for data. You may also need to allow data roaming for that line specifically: the toggle is per line, so switching it on for the eSIM does not switch it on for your home number. Then turn mobile data off on your home line and leave its calls and texts running. The whole thing usually finishes before the seatbelt sign does.

Everything you want in the first hour is data work anyway. Ticket machines and app bookings for the Skyliner, the Narita Express, the Keikyu line from Haneda or the Limousine Bus, the exact exit number at your destination station, and the hotel address in Japanese to show a taxi driver. Kansai arrivals will be doing the same for the rail run into Osaka.

The networks you'll be on

Your phone attaches to KDDI, which runs 4G/LTE and 5G in Japan. You do not choose between them: the handset takes whatever the tower offers where you are standing and hands off as you move. In practice 4G/LTE does most of the work, and 5G turns up around big-city cores and major stations.

Nothing on your side changes when the generation changes, so there is no setting to fiddle with. If a page stalls, it is far more often a long tunnel or a packed stadium than a network problem.

Where coverage holds, and where it thins

Urban Japan is about as easy as connectivity gets. Tokyo, Osaka, Nagoya, Fukuoka and Sapporo hold signal at street level, down on subway platforms, and inside the department stores and station complexes you will spend a surprising amount of time in. The Shinkansen keeps you online for most of a run, with drops in the long tunnels between cities; the Tokaido route through the mountains is where you notice that most.

It gets patchier once you leave the corridor. The Japanese Alps around Kamikochi and Takayama, the Kumano Kodo trails, the interior of Hokkaido away from the main roads, and the small islands off Okinawa are all places to expect gaps rather than be annoyed by them. Ferries lose signal partway across. Temple districts in Kyoto and Nara are fine: you are outdoors and close to town.

What you'll actually use data for here

Transit routing is the big one. Maps and the Japanese transit apps give you the platform, the transfer, the exit number and the last departure of the night, and that last detail saves an expensive late taxi more often than travellers expect.

Translation is second. Pointing a camera at a ramen ticket machine, a supermarket label or a box from the pharmacy does more for you than a phrasebook ever will. Then the wallet layer: adding a Suica to Apple Wallet or Google Wallet and topping it up both need a live connection, and you will top it up more often than you think.

The rest is small and constant. Booking a table somewhere that does not really do walk-ins, checking what time a ryokan wants you in for dinner, tracking a suitcase you sent ahead by luggage forwarding, and working out which convenience store nearby has a cash machine that will accept a foreign card.

Before you fly

Check that your phone is eSIM capable and not locked to your home carrier. A locked handset will refuse the profile no matter what you try at the airport, and that is not a problem you want to discover in Japan.

Download offline maps for anywhere mountainous on your route, and screenshot the things you cannot afford to lose: your accommodation address in Japanese, seat reservations, and the pickup details for anything booked ahead.

Bring a power bank. Days here run long, navigation plus camera use drains a battery fast, and Japanese trains are not littered with sockets. Last thing: switch off your home carrier's data roaming before boarding, so the only line carrying data is the one you meant to use.