5 Top Japan SIM Cards Compared: Stay Connected

The Right SIM Card Makes Your Japan Trip Smoother

For Hongkongers, Japan often feels like a second home—whether for cherry blossoms, shopping, skiing, or hot springs, it’s a favorite travel destination. But losing internet access during a trip can be a nightmare—no maps, no reservations, no contact with family.

Japan SIM card choices are abundant. Common brands include Joytel Gold, Softbank native SIM, Docomo IIJmio SIM, China Unicom, and newcomers like b4travel. Although many are labeled as “unlimited,” real-world experiences can vary greatly—especially during peak travel times, where daily-capped plans and native high-speed SIMs perform very differently.

Let’s break down what matters and help you pick smartly.

Common Types of Japan SIM Cards / eSIMs

Overview of Japan’s Big Three Telecom Providers

Japan’s top three mobile carriers are NTT Docomo, SoftBank, and KDDI (au). They offer the best coverage and speeds nationwide, with both native SIM and eSIM services. There are also many MVNOs (Mobile Virtual Network Operators) like IIJmio, DJB, bmobile, which lease bandwidth from these carriers to offer cheaper services.

Docomo vs. IIJmio

Docomo is Japan’s largest carrier, known for strong signals and extensive 5G coverage. Native Docomo SIMs/eSIMs are perfect for long trips or heavy internet usage. But beware—many SIMs claiming to use Docomo's network are actually MVNOs like IIJmio. While they connect to Docomo, they only rent part of its bandwidth, meaning they’re more prone to slowdowns or disconnections during rush hours or in crowded places.

Learn more Docomo

Softbank

SoftBank performs very well in major cities like Tokyo and Osaka. Their native SIMs and premium plans (like Joytel Gold) maintain stable signals in busy areas. While Softbank might not be as strong in rural regions as Docomo, their speeds are still impressive overall.

Learn more Softbank

KDDI (au)

KDDI (au) is Japan’s second-largest carrier. It offers stable speeds and broad 4G/5G coverage. Its biggest strength lies in balancing performance and cost, ideal for casual travelers not venturing into remote areas. However, performance may slightly drop indoors or in mountainous regions.

Learn more KDDI (au)

What is MVNO? Is It Worse?

MVNOs like IIJmio, DJB, b4travel, China Unicom don’t operate their own networks. Instead, they lease bandwidth from big providers like Docomo, Softbank, or KDDI—so they’re cheaper. However, their connections are not prioritized, meaning speeds can drop significantly during busy periods or at night.

2025 Performance Test: How Popular Japan SIM Cards Stack Up

1. Joytel Gold SIM

• Network: SoftBank / KDDI

• Price: ~HK$60

• Speed: 70–100 Mbps in cities; 40 Mbps in Ueno subway

• Features: No throttling, stable signal, supports hotspot

• Best For: Users who value speed and stability

2. Softbank 15GB Native SIM

• Network: Softbank

• Price: ~HK$95, no expiration

• Ideal for: Two short trips to Japan; flexible usage

• Coverage: Still gets 5G in Chiba/Yokohama; mostly 4G in cities

3. Docomo IIJmio SIM

• Network: Docomo (via IIJmio)

• Price: ~HK$45

• Speed: 20–40 Mbps by day, drops to ~10 Mbps during peak hours

• Best For: Light users on a budget

• Note: Not ideal for multitasking due to speed drops

4. Docomo IIJ 5G SIM

• Network: Docomo

• Price: ~HK$58

• Speed: Similar to above

• Best For: Budget-conscious high data users
  
  

5. China Unicom 8-Day 8GB (5G Support)

• Price: ~HK$60

• Stable signal, supports tethering

• Post-limit speed suitable for browsing, not streaming/navigation

• Bonus: Includes call function (outbound only); no Japan number (can’t receive calls or make local reservations)

Conclusion: The Right SIM Means a Smoother Trip

Whether you're visiting Japan for the first time or are a seasoned traveler, picking the right SIM card makes all the difference. Use this guide to make a smart choice based on your trip length, data needs, and budget.

Where to buy Japan SIM cards?

• Visit the Expandus online store

• Or stop by a physical location