This actually happened a couple of weeks ago, but it is Akinori Iwamura’s first home run at any level since he hit three for the Indianapolis Indians, the Pirates triple-A affiliate, in 2010. Aki returned to Japan last year, signing with the Tohoku Rakuten Golden Eagles, but he did not hit a home run in 77 games. This year he is hitting .215 with a .325 OBP in 24 games.
Of course, Aki hit 14 home runs in 2.5 seasons with the Rays and was a key member of the 2008 American League champions. That came after he hit 106 home runs in the three seasons prior to signing with the Rays.