Why International eSIMs Fail in Tokyo Subways — And How to Stay Connected

“No signal as soon as I enter the subway,” “The map won’t load,” “Have to reconnect every time I leave a mall”—have you experienced these too? More and more travelers using international eSIMs have taken to Reddit and Instagram to complain: even though they purchased an eSIM for Japan, they found themselves completely disconnected in Tokyo subways, shopping malls, or high-rise buildings. Google Maps freezes, transit info becomes inaccessible, and even contacting friends gets difficult.

Why Do International eSIMs Often Lose Connection in Japan?

Most international eSIM brands use Cloud SIM technology, meaning they aren’t tied to a specific carrier but automatically connect to the strongest available local network, such as SoftBank, au, or docomo. This sounds convenient in theory, but in reality, these eSIMs are not in direct partnership with Japanese carriers—they connect via international roaming agreements. As a result, when entering places with weak signal like subways or basements, the eSIM may not switch to a stable network quickly enough, leading to temporary or prolonged disconnections.

Why Are Tokyo Subways, Underground Malls, and High-Rises Signal Dead Zones?

Urban areas in Japan are densely built, and underground spaces are layered and complex. Many subway stations are located dozens of meters below ground—particularly on lines like the Ginza Line, Marunouchi Line, and Hibiya Line. Roppongi Station on the Oedo Line is even known as one of the deepest subway stations in the world. Many segments of the subway lie more than two levels underground, crisscrossed by utility infrastructure. If your eSIM isn’t directly connected to a main local network but relies on international roaming, it’s natural for the signal to be lost or for reconnection to fail in such environments.

For example:

• In Tokyo subway transfer areas: phone maps fail to show floor levels and navigation freezes.
• In Shinjuku or Shibuya underground malls: entering the area leads to a complete signal drop, even QR code payments fail.
• Inside elevators or high-rise buildings: poor signal penetration leaves you with barely one bar of reception.

Why Is CDJapan Rental's Local eSIM Less Prone to Disconnections?

CDJapan Rental provides a Japan-based eSIM, not an international Cloud SIM. It connects directly to the docomo network—one of Japan’s top three telecom providers—without going through third-party intermediaries. This results in better performance for signal penetration and base station coverage. In field tests on lines like the Ginza Line, Marunouchi Line, and Yurakucho Line, users were still able to access maps and send messages smoothly.

This type of local eSIM not only maintains stable connections inside the subway but is also ideal for travelers who heavily rely on mobile navigation, translation, and communication tools.

Recommended for Those Tired of Losing Signal: A More Stable eSIM

If you’ve ever been driven crazy by connection issues while traveling, we recommend choosing an eSIM plan that uses a local Japanese telecom network, such as those offered by CDJapan Rental:

• Unlimited Data eSIM for 5, 10, or 15 Days: Ideal for short-term trips
• High-capacity eSIM for 31 or 91 Days: Great for longer stays

All of these plans support hotspot sharing. No shipping or pickup required—as long as you have Wi-Fi (even free Wi-Fi is fine), you can place your order and install it. Even if you’re already in Tokyo, you can activate it immediately.

Conclusion: Choose the Right eSIM, and Stay Connected Throughout Tokyo

Losing signal in the subway is truly frustrating, but in many cases, it’s not that Japan’s network is poor—it’s that your eSIM isn’t suitable for local use. Choosing an eSIM that supports direct local connections and doesn’t switch between networks ensures stable internet access in Tokyo’s subways, skyscrapers, and underground malls.

FAQ: More About eSIMs in Japan