Japan's three major carriers — NTT Docomo, au (KDDI) and SoftBank — each run extensive 4G and 5G networks, with a fourth, Rakuten Mobile, expanding more recently. Docomo is generally regarded as having the broadest rural and mountain-area reach, connecting in places like Shikoku's pilgrimage routes, deep Tohoku and smaller onsen towns where other carriers can thin out; SoftBank and au are typically strongest in the major cities. Coverage in Tokyo, Osaka, Kyoto and other large cities is excellent across all three, including underground subway stations and dense urban canyons, and 5G is widely available in metropolitan areas, though rural coverage still relies mainly on 4G.

Japan has a genuinely distinct connectivity culture compared with most countries: pocket WiFi rental — a small battery-powered router picked up (often pre-booked) at the airport and shared across several devices — has long been the standard recommendation for families, groups, or anyone travelling with a laptop, while a data-only eSIM has become the default for solo travellers and couples with a single compatible phone, since it activates before landing with nothing to carry, charge or return. Most standard tourist SIMs and eSIMs bought from Japanese sources are data-only and do not include a Japanese phone number, so apps requiring SMS verification tied to a Japanese number, or services like PayPay that expect one, are a separate consideration regardless of which data option is chosen.

Japan's Telecommunications Business Act requires identity verification — commonly called eKYC — for SIMs and eSIMs issued directly by a Japanese carrier, typically a passport photo uploaded through an app or shown at a counter. This requirement applies to local carrier products; a travel eSIM purchased from an international provider before departure is a roaming service rather than a Japan-issued line, so it is not subject to the same eKYC step, and no passport data is submitted to a Japanese carrier at all.

The practical sequence: install the eSIM profile over Wi-Fi before the flight, keep the home SIM active for calls, SMS and any service that needs a home-country number, and switch on the data eSIM once landed at Narita, Haneda or Kansai.

A SIM or eSIM bought directly from a Japanese carrier requires eKYC identity verification — a passport photo, submitted via an app or shown at a counter — under the Telecommunications Business Act. A travel eSIM from an international provider is a roaming product rather than a Japan-issued line, so this step does not apply to it. Either way, most tourist data products in Japan are data-only with no Japanese phone number, so the home SIM remains the line for calls, SMS and any local-number-dependent service.