Koike played outfield and infield for the Chunichi Dragons (2008–2011) and for the Yokohama DeNA BayStars (2012–2013).

Koike announced his retirement on October 1, 2013 and his final at-bat, hit a home run.

In 2014, the Yokohama DeNA BayStars hired Koike as first team batting coach.

On 6 November 2024, it was confirmed Koike had accepted an offer to become a hitting coach for the Chunichi Dragons.

This biographical article relating to a Japanese baseball infielder is a stub.