Valentine managed the Chiba Lotte Marines to the 2005 Japan Series title while Nishioka was an All-Star four times under his watch from '05-08.
"You know, I had him as a baby in Japan," Valentine said. "I had him where he was one of the worst players on the field and had him when he was one of the best players on the field. And sometimes it was in the same season."
Valentine was dismissed after the 2009 season, and Nishioka ended up having a breakout year in '10, winning the battle en route to claiming another Japan Series title.
He signed a three-year deal worth $9.25 million with the Twins before last season, but struggled in his first year, hitting just .226 with a .527 OPS in 68 games. His first season was marred by injuries, including a broken left fibula suffered on April 7 when Nick Swisher slid into him at second base trying to break up a double play.
Nishioka missed 59 games because of the injury, but Valentine said it could've been prevented because he tried to warn him that players in the Majors try to break up double plays with hard slides not seen in Japan.
"I came to Fort Myers last year to have dinner with him, to tell him they were going to try and break his leg and show him how to try and get out of the way, because he didn't do that in Japan when he played second base for me his first year," Valentine said. "I actually got up and showed him where he had to be on that double play, because in Japan you don't have to worry about the inside slide, only the outside slide.
"A guy comes inside and rolls, he had to be out of the way, and he gave me the old -- as he did as a player for me -- 'Yeah, yeah, yeah, I understand. I understand. I understand.' And he broke his leg."