NEW YORK, Jan. 12 -- A legal battle between two of Japan's highest-profile tech entrepreneurs potentially looms following the arrest of a Rakuten Mobile employee over the alleged theft of sensitive SoftBank data.

Tokyo police arrested 45-year-old Kuniaki Aiba on Tuesday, under suspicion of breaching the Unfair Competition Prevention Law.

Aiba, who had worked for SoftBank Corp. for 15 years prior to joining Rakuten, is alleged to have illegally taken files relating to SoftBank's 5G, 4G and backhaul networks, Japan News reports.

In a statement, SoftBank Corp. said it believed Rakuten Mobile was in possession of its network data and "is likely to have already used our trade secrets in some way."

It said it would file a lawsuit to ensure ...