Updated: 2025-11-19 17:25:40
When preparing for a trip to Japan, securing a "reliable internet connection" is just as important as booking your hotel or airline tickets.
Whether it's searching for routes on Google Maps, using translation apps, or posting to social media, a smartphone is essential for a comfortable trip. Many travelers to Japan stick with their home country's carrier plan to connect while in Japan. Recently, many people also purchase services that handle eSIMs for various countries, such as the popular "Holafly" or "Airalo." However, you may encounter situations in Japan where the "connection is slow," "Japanese apps won't work," or "websites won't open." This is actually because the data is being transmitted via roaming.
In this article, we will explain the downsides of using an eSIM via "roaming" and why you should choose a "Japanese local eSIM" that connects directly to the Japanese network.
If you are thinking, "It's too much of a hassle, so I'll just use my current phone as-is in Japan," please wait a moment. There are three major risks to turning on "Data Roaming" with your home carrier's settings.
If you aren't on an international flat-rate plan, just receiving emails or loading maps could result in a bill of hundreds or thousands of dollars after you return home.
Even with an "unlimited" plan, it is common to face strict limits when abroad, such as "up to 500MB per day." Once you exceed this, speeds become extremely slow.
Because your phone is constantly searching for the optimal signal in unfamiliar territory, your battery will drain much faster than usual.
If you search for "Japan Travel eSIM" on Google, you will find services selling eSIMs usable in Japan or multiple countries. These seem to be popular lately. However, did you know that "when you use data during your stay, even though you are in Japan, your connection is routed all the way through a foreign country"? Many of these eSIMs operate via roaming.
You
→
Japanese Base Station
→
Overseas Server
(Hong Kong, Europe, etc.)
→
Japanese Website
※Because data travels through a foreign country, delays occur. Also, services exclusive to Japan may become unusable.
The solution to the problems caused by roaming eSIMs is a "Local eSIM" provided domestically by a Japanese telecommunications operator.
If you purchase an eSIM sold by a Japanese company for use in Japan, you won't face restrictions common with roaming, such as being unable to view web pages or purchase items.
Direct connection to Japan servers means low latency. Maps and search load instantly.
You can use Japanese payment services and reservation sites without being blocked.
Genuine Docomo or SoftBank network quality.
We recommend "CDJapan Rental" for travelers to Japan, a service with over 20 years of experience. They provide "fully local Japanese connectivity" that does not pass through overseas servers.
| Feature | Home Carrier Roaming |
Cheap Overseas eSIM |
CDJapan Rental (Local) |
|---|---|---|---|
| Cost | High | Reasonable/Cheap | Cheap |
| Response Speed (Ping) | Slow | Slow (Via Overseas) |
Very Fast (Direct Japan) |
| IP Address | Home Country | Overseas | Japan |
| Japanese Apps (PayPay etc.) |
Partially Unusable | High Chance of Blocking |
All Usable |
| Recommendation | ▲ | ● | ★ |
Don't just choose based on "as long as it connects," only to end up stressed once you arrive.
To enjoy your limited time in Japan to the fullest, buy a Japanese eSIM.
