TOKYO - Rakuten Mobile faces a new test of its network quality after KDDI decided to scale back roaming support from September 2026, ending access to its network in areas where Rakuten already has its own base stations while continuing service in mountainous and sparsely populated regions.
Rakuten Mobile entered Japan's mobile phone market in earnest in April 2020 as a latecomer competing with NTT Docomo, KDDI's au and SoftBank.
Because its own network was initially limited, Rakuten relied on KDDI roaming to supplement coverage in areas where construction of its base stations had not kept pace.
The arrangement is due to expire in September 2026, and KDDI has decided to reduce the areas where its network is made available to Rakuten.
Under the new policy, roaming will generally be terminated in areas where Rakuten Mobile already operates its own base stations.
KDDI President Hiromichi Matsuda has said traffic from Rakuten users has grown more than expected, increasing the load on KDDI's network and potentially affecting the quality of services provided to its own customers.
Rakuten Mobile has expanded rapidly and now has more than 10 million mobile lines.
Its growth has also drawn criticism from rivals that say the company has prioritized subscriber acquisition while relying on another operator's network rather than investing sufficiently in its own infrastructure.
SoftBank previously criticized Rakuten after it said it would avoid raising prices, arguing that other carriers were having to reflect the cost of building and maintaining extensive base station networks in their pricing.
The effect of KDDI's roaming reduction is likely to vary by area.
KDDI publishes a map showing where it provides roaming service to Rakuten Mobile. Information updated on June 1, 2026, showed coverage in a number of cities and towns outside Tokyo's 23 wards.
Roaming areas also included locations where large numbers of people gather, including around Maihama Station in Urayasu, Chiba Prefecture, near Tokyo Disney Resort, and parts of the Minato Mirai district in Yokohama.
Not all such areas are expected to lose roaming immediately, but KDDI's coverage is expected to shrink progressively.
Ministry of Internal Affairs and Communications data showed a substantial gap in network infrastructure as of the end of March 2025.
NTT Docomo, KDDI and SoftBank each had roughly 300,000 to 400,000 base stations, compared with just over 100,000 for Rakuten Mobile.
Rakuten says roaming will be ended only in areas where its own network can provide sufficient coverage.
Rakuten Group Chairman and CEO Hiroshi Mikitani said in a post on X that the company would continue providing services customers can use with confidence.
Even so, any deterioration in connectivity in crowded areas could quickly damage Rakuten Mobile's reputation.
For mobile operators, perceptions that a network is difficult to connect to can be particularly damaging because poor connectivity is a major reason customers switch carriers.
Rakuten plans to spend 200 billion yen this year on base station construction as it works to strengthen coverage.
KDDI, meanwhile, has strong incentives to protect the performance of its own network.
In its April-June 2026 results, the company said restructuring efforts in its mobile business were producing results.
KDDI had 33.3 million smartphone subscriptions at the end of June 2026, up 390,000 from a year earlier.
Its churn rate fell by 0.06 percentage point to 1.17%.
The company has been attracting users through lower-priced brands such as UQ mobile and povo and then encouraging some customers to move to the main au brand, helping build longer-term relationships.
Allowing Rakuten traffic to place greater strain on KDDI's network could risk undermining that strategy if au or UQ mobile customers experience poorer service.
KDDI was originally created in part to challenge NTT's dominance in Japan's telecommunications market, and it initially had an incentive to support Rakuten as another company seeking to increase competition.
However, with Rakuten Mobile's subscriber base now exceeding 10 million lines, the company has increasingly become a direct rival rather than a fledgling entrant.
Rakuten Group itself has only recently begun showing signs of a financial recovery after years of heavy spending on its mobile business.
Its consolidated results for the first half through June 2026 showed an operating profit for the first time in seven years, since 2019.
The mobile business had been a major reason for the group's prolonged operating losses because of the heavy investment required to build its network.
If customers begin to view Rakuten Mobile as harder to use because of reduced roaming coverage, the company could be forced to accelerate investment further, putting renewed pressure on earnings.
The issue could also extend beyond the mobile business because Rakuten has built a broad economic ecosystem spanning services such as banking, securities, e-commerce and telecommunications.
If dissatisfaction with Rakuten Mobile causes customers to leave the service, it could also weaken the company's ability to retain users across the broader Rakuten ecosystem.
Source: Kyodo
