He only stole 5-8 bases per year for the last 5 seasons. Career high of 15 came in 2001 before he became a true power threat in Japan. He might adjust his game to incorporate more speed upon starting his MLB career (like Ichiro who only stole 11-21 bases per year in his last three years in Japan) because he probably also knows that Japanese hitters tend to get their HR totals halved when moving across the Pacific.
http://japanesebaseball.com/players/pla ... ayerID=993