Wireless carrier SoftBank Corp. said Thursday it had filed a damages suit against a former employee and its rival Rakuten Mobile Inc. for illegally using the plaintiff's 5G network technology information, leaked by the ex-SoftBank worker.

In the lawsuit filed with the Tokyo District Court, SoftBank Group Corp.'s mobile phone service subsidiary is seeking ¥1 billion ($9.1 million) as part of alleged damages totaling about ¥100 billion, it said.

SoftBank is also demanding suspension of the use of Rakuten's base stations, which have allegedly been built based on the leaked information, and that they be scrapped.

In response to the legal action, Rakuten said it has not confirmed any use of SoftBank's trade secrets in its internal investigation and will present its views in the upcoming court hearings.

In January, police arrested Kuniaki Aiba, who joined Rakuten Group Inc.'s wireless unit soon after leaving SoftBank in December 2019, on suspicion of having transferred data on the plaintiff's 5G technology to his own email account in violation of Japan's unfair competition prevention law.

SoftBank said in a press release that Rakuten once had electronic files containing SoftBank's trade secrets on its server. Rakuten said the files had been abandoned after submitting them to the court and the plaintiff, according to SoftBank.

In September last year, Rakuten started offering unlimited data services using ultrafast 5G networks for ¥2,980 per month, much lower than other major mobile phone service operators in Japan amid intensifying competition.

Rakuten entered the wireless market in October 2014 as a virtual mobile network operator, using other mobile phone operators' networks, and started full-scale services with its own networks last year.