A former employee of SoftBank Corp. was arrested Tuesday on suspicion of taking information from the major Japanese wireless carrier on its ultrafast 5G technology before moving to a smaller rival company, police said.

The arrest of Kuniaki Aiba, who currently works for wireless operator Rakuten Mobile Inc., comes amid intensifying competition among mobile companies in Japan due partly to the government's pressure to cut subscription fees.

A Rakuten Mobile Inc. branch in Tokyo's Ginza district. (Kyodo)

While Japan's three major mobile carriers -- SoftBank, NTT Docomo Inc. and KDDI Corp. -- launched 5G services, which enable the transmission of movie and other large capacity data at a faster speed than the 4G system, in March last year, Rakuten Mobile joined the race in September and still lags behind its bigger rivals.

Aiba, 45, is suspected of having transferred trade secrets from SoftBank by emailing information on the company's 5G technology to his personal account on Dec. 31, 2019, his final day at the company, in violation of Japan's unfair competition prevention law, according to the Tokyo police.

He joined the mobile business unit of e-commerce giant Rakuten Inc. the next day on Jan. 1, 2020.

Jun Shimba, chief operating officer of SoftBank Corp., speaks at a launch event in Tokyo on Dec. 22, 2020. The wireless carrier unit of SoftBank Group Corp. announced a new lineup of cheaper options for data usage from March 2021. (Kyodo) 

SoftBank said the former employee, who joined in 2004, had been engaged in building networks and took information on 4G and 5G base stations as well as SoftBank's communication networks. It added he did not steal customer information.

SoftBank believes Rakuten Mobile has already used the information, which might be preserved in Aiba's business computer at Rakuten, and plans to file a lawsuit demanding its rival stop using the information and destroy it.

Rakuten Mobile said in a release that the trade secrets do not include information about SoftBank's 5G system and its internal probe has not confirmed they were used for its business.

"We will fully cooperate with the police investigation to get the bottom of the matter," Rakuten Mobile said.

Softbank contacted the police in March. Aiba's home and Rakuten mobile were searched in August.

Japanese mobile companies have been strengthening their 5G services as a new source of profit amid Prime Minister Yoshihide Suga's call for lowering their fees that he has said are higher than those in some other countries.

Although those companies have rolled out cheap 5G plans, their ultrafast services are currently available in large cities and some other limited areas.

The newcomer, Rakuten Mobile, is facing an uphill battle as it is still working on setting up its 4G networks, in addition to 5G networks, industry officials said.

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