Quick Answer
au by KDDI serves 71.46 million subscribers in Japan with the best urban 5G performance and 13-language customer support. SoftBank has 56 million subscribers and the Y!mobile budget sub-brand. au has a faster 5G network. SoftBank offers better budget options through Y!mobile.
Side-by-Side Comparison
This table compares Japan’s second and third largest mobile operators.
| Feature | au (KDDI) | SoftBank |
|---|---|---|
| Subscribers | 71.46 million | 56 million |
| 5G Performance | Best in urban areas | Good, growing |
| Fiber Brand | au Hikari (1 Gbps) | SoftBank Hikari |
| Budget Sub-brand | UQ mobile | Y!mobile |
| Language Support | 13 languages | Japanese primary |
| Technology | 5G, 4G LTE, FTTH | 5G, 4G LTE, FTTH |
| Strength | Urban 5G, multilingual | Y!mobile value, ecosystem |
Test au speed | Test SoftBank speed
Speed Comparison
au by KDDI delivers the fastest 5G speeds in Japanese cities. KDDI’s dense urban small-cell deployment gives au an edge in Tokyo, Osaka, Nagoya, and Fukuoka. Download speeds on au 5G regularly exceed SoftBank in urban speed tests.
SoftBank’s 5G network is growing but trails au on urban throughput. SoftBank compensates with aggressive pricing and its Y!mobile sub-brand, which offers solid 4G speeds at lower monthly cost.
Both operators offer fiber broadband. au Hikari delivers 1 Gbps. SoftBank Hikari provides similar speeds. Home broadband performance is comparable between the two.
Run a speed test to check your actual speeds on either network.
Coverage
au focuses 5G deployment on profitable urban corridors. Major cities get dense au 5G. Rural coverage is adequate on 4G LTE but 5G availability drops outside cities.
SoftBank has a similar urban-focused approach. Neither au nor SoftBank matches NTT DoCoMo for rural 5G coverage (70% population).
Both operators provide near-complete 4G LTE coverage across Japan. The 5G availability difference matters mainly in mid-sized cities and suburban areas.
au’s 13-language support is a major differentiator for foreign residents. SoftBank primarily serves in Japanese, making au the better choice for English, Chinese, Korean, and other language speakers in Japan.
Which Should You Choose?
au by KDDI suits users who want the fastest urban 5G and need multilingual support. The 13-language customer service is unmatched among Japanese carriers. If you live in a major city, au’s 5G network gives the best mobile experience.
SoftBank suits budget-focused users through Y!mobile. Y!mobile plans start lower than au’s UQ mobile equivalent. SoftBank also integrates well with Yahoo Japan and PayPay ecosystem services popular in Japan.
For the widest coverage, especially rural areas, compare NTT DoCoMo with 91.91 million subscribers and 70% 5G coverage.
Summary
au leads on urban 5G speed and multilingual support (13 languages). SoftBank competes on price through Y!mobile and its digital ecosystem. Both are strong urban networks. Choose au for speed and language support. Choose SoftBank for Y!mobile budget plans.
Test your connection at Kencang speed test and see the Japan internet overview for the full market picture.
Last Updated: March 28, 2026 Data Sources: TCA Japan subscriber data, Opensignal Japan report, operator announcements