Twins general manager Terry Ryan said he was aware of the report, but said he hadn't heard anything official about Nishioka signing with Hanshin. The details of his contract are unknown.
Nishioka was granted his release by the Twins on Friday, as he opted to walk out on the rest of his contract. He was owed $3 million next season, and the Twins held a $4 million club option for 2014, with a $250,000 buyout.
Nishioka, 28, struggled with the Twins after signing a three-year deal worth $9.25 million after Minnesota won the negotiating rights to sign him with a $5.3 million bid in 2010. He hit just .215/.267/.236 in 71 games over the last two years, while looking uncomfortable defensively.