au (KDDI) in Japan: Coverage & Tips for Travellers

eSIM from 1,00 USD · 100 MB. Networks: KDDI/au (5G), NTT docomo (4G), NTT docomo (5G), Rakuten Mobile (5G), SoftBank (5G).

au (KDDI) in Japan

Best for: Balance of speed and coverage

What to know

• Good nationwide reach and competitive in cities
• Strong in western Japan (Kansai, Kyushu)

Areas where signal can drop

• Deep mountain areas (Nikko and Hakone lake districts)
• Remote islands (Yakushima, Iriomote in Okinawa)
• Some train tunnels on scenic rural lines
• Basement floors of dense Tokyo electronics districts

Other carriers in Japan

• NTT Docomo : Widest coverage including rural Japan
• SoftBank : Urban speeds and 5G

If you have no signal (quick troubleshooting)

1. Aeroplane mode for 10 s → disable.
2. Confirm the eSIM line is set as "Mobile Data".
3. Restart your phone.
4. Settings → Network → Manual network selection → choose au (KDDI).
5. If nothing works: check the APN (sometimes needs manual configuration).

Quick checklist: stay online without surprises

The make-or-break moment is often the first 30 minutes after landing: maps, transport, messages. Install your eSIM on Wi‑Fi before you travel and switch mobile data to the eSIM when you arrive. That way you're not dependent on airport Wi‑Fi and you avoid accidental roaming charges.

For typical use (maps + messaging + light social media), 1–3 GB per week is often enough. If you tether for a laptop, take video calls, or stream daily, aim for 10 GB+ or a plan with fair-use throttling instead of a hard cut-off.

• Networks: KDDI/au (5G), NTT docomo (4G), NTT docomo (5G), Rakuten Mobile (5G), SoftBank (5G)
• Offline maps: download the area in Google Maps, Apple Maps, Yahoo! Japan Maps while you're on hotel Wi‑Fi.
• On the move: GO (taxi), S.RIDE, DiDi Japan + LINE, WhatsApp work well on low data — video and app updates are usually the real data drains.
• Common weak spots: Deep mountain areas (Nikko and Hakone lake districts) · Remote islands (Yakushima, Iriomote in Okinawa)
• City context: Tokyo: Excellent coverage; Metro LTE on most lines; dense buildings can blip indoors. · Osaka: Strong 4G/5G; Dotonbori and Namba districts well-covered.

Phone setup tip: keep your primary SIM active for calls/SMS (so 2FA codes can arrive), but turn off mobile data on that line. Set the eSIM as your data line — it prevents accidental roaming on the wrong SIM and keeps WhatsApp/banking flows more predictable.

Current eSIM plans (examples)

Examples from our database — availability and pricing can change.