eSIMs for Japan
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There are about forty pages telling you the best eSIM for Japan and they mostly rank the same five products by price. Price is the least interesting thing about them. What decides whether your data works in a valley in Hakone or a train through the Kiso is which Japanese carrier your eSIM actually runs on – and most providers will not tell you.
Japan has three networks that matter: NTT Docomo, KDDI au and SoftBank. Docomo has the best rural footprint. Of the five providers below, exactly two name their carriers on their own site.
At a glance
- Cheapest small plan
- Saily, 1GB/7 days, $3.99
- Best disclosed network
- Ubigi – the only one naming Docomo on its own site
- Most generous daily cap
- Saily, 5GB/day before throttling
- Only one with a phone number
- Saily, as a paid add-on
In this guide
Which network each one actually runs on
| Provider | Japanese network | Daily cap before throttling | Tethering |
|---|---|---|---|
| Ubigi | KDDI + NTT Docomo, named on their own site | 30GB over 15 days, then 2 Mbps | Yes |
| Nomad | KDDI + SoftBank up to 10GB; KDDI only above 10GB | 2GB/day | Yes, uncapped |
| Saily | KDDI + SoftBank | 5GB/day, then 1 Mbps | Yes |
| Airalo | SoftBank “and 1 other” – not disclosed | 3GB/day, then 1 Mbps | Yes, uncapped |
| Holafly | KDDI / SoftBank, no choice | No published cap | Yes, but 1GB/day hotspot limit |
Two things fall out of that table. Nomad's large plans are the trap: buy more than 10GB and you are on KDDI only, which is the carrier with the weaker mountain and coastal coverage – exactly where you were going if you bought a big plan. And Holafly's unlimited is not unlimited for a hotspot; the 1GB daily tethering cap is the real limit if you are sharing to a laptop.
Nobody sells a traveller eSIM on Rakuten. If you want Docomo specifically and reliably, Ubigi is the one that says so in writing.
When to activate it
Install before you fly, activate when you land. Installing the profile is a download over your home wi-fi and costs no data; it does not start the clock. Validity almost always begins at first connection to a Japanese network.
Almost always, not always. Airalo states that some of its eSIMs activate on install regardless of where you are, with the rule shown in each product's own notes before you buy. Read that line for your specific package rather than trusting the general advice, including ours.
Do not try to install in the air. Onboard wi-fi is too slow and unstable for a profile download, and a half-downloaded profile is worse than none.
What actually goes wrong
The failures are boringly consistent and almost none of them are the eSIM's fault.
A carrier-locked handset. The single most common one. If your phone is locked to a home network it will not register on Docomo, KDDI or SoftBank. Unlocking typically takes one to three business days, so this is a thing to check a week out, not at the gate. A phone still on a carrier payment plan usually stays locked until the plan finishes.
A phone with no eSIM hardware at all. Different problem, same outcome. Mainland-China iPhone and Samsung variants physically lack it. Jailbroken and rooted devices are blocked.
Data still routed to the home SIM. On a dual-SIM phone the eSIM installs perfectly and mobile data stays on the old line. Check which line is set for data, not just that the eSIM is there.
Roaming off, or the line not switched on. Both need to be enabled. After landing, give it a minute or two, then toggle airplane mode if nothing has attached.
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Frequently asked questions
Which eSIM has the best coverage in rural Japan?
On the published evidence, Ubigi – it is the only provider that names NTT Docomo on its own site, and Docomo has the strongest rural footprint. Be careful with large Nomad plans: above 10GB they are KDDI only.
Do I need to activate my Japan eSIM before I fly?
Install it before you fly, activate on arrival. Installing is a download and costs nothing; validity normally starts at first connection to a Japanese network. Check your specific package's notes, because a few activate on install.
Is an unlimited Japan eSIM really unlimited?
No. Every “unlimited” plan here throttles after a daily allowance: Saily at 5GB a day, Airalo at 3GB, Nomad at 2GB. Holafly publishes no daily cap but limits hotspot use to 1GB a day.
Can I get a Japanese phone number with an eSIM?
Of the five here, only Saily, and only as a paid add-on. The rest are data-only. If you need a number for restaurant bookings, Sakura Mobile and Mobal sell voice plans on Docomo.
Will my phone work in Japan?
If it is unlocked, eSIM-capable and not a mainland-China variant, yes. Carrier locking is the most common failure and takes one to three business days to undo, so check before you travel.
Further reading
Official sources
- Ubigi – Japan data plans – Names KDDI and NTT Docomo; plan prices
- Nomad – best eSIM for Japan – The over-10GB KDDI-only rule
- Saily – Japan eSIM – 5GB/day cap, phone-number add-on
- Airalo – unlimited fair use policy – 3GB/day then 1 Mbps
- Holafly – Japan eSIM – 1GB/day hotspot limit
- Airalo – device compatibility – Carrier lock and unsupported devices