In a rare move by a player, Nishioka approached the Twins about the release and is walking away from 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.
"I would like to thank the Twins organization for helping me fulfill my dream of playing in Major League Baseball," Nishioka said in a statement. "I take full responsibility for my performance, which was below my own expectations. At this time, I have made the decision that it is time to part ways. I have no regrets and know that only through struggle can a person grow stronger. I appreciate all the support the team and the fans in Minnesota and Rochester have shown me. Arigatou gozaimasu."
Nishioka, 28, has struggled with the Twins since 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.
Nishioka hit just .226/.278/.249 with five doubles in 68 games last year, as he missed more than two months after breaking his left leg in a collision at second base in just the sixth game of the season.
Nishioka came into this season fighting for a spot on the roster but was sent to Triple-A Rochester in the first round of cuts in Spring Training.
After hitting .245 in 84 games with the Red Wings, Nishioka was given another chance with the Twins, when he was called up on Aug. 5.
But Nishioka lasted just three games with the Twins before being sent back down, as he went 0-for-12 with several miscues in the field at second base. He was later outrighted on Aug. 20 and was removed from the 40-man roster.
It was a disappointing two years for Nishioka, who excelled in Japan. The switch-hitter was a five-time All-Star and three-time Gold Glove winner with the Chiba Lotte Marines before signing with the Twins.