Imaoka spent several uneventful seasons in the Japanese professional leagues before being chosen as the lead-off batter by Senichi Hoshino, who managed the Hanshin Tigers from 2002-2004. Imaoka won the batting title in 2003 with a .340 batting average, and his team won the Central League pennant the same year. He had previously played shortstop and second base, but was converted to third base in 2004. He continued his hitting prowess, and led the league with 147 RBIs in 2005. He fell into a huge slump in 2006, and missed half of the season due to injuries.
He won a silver medal playing for the Japanese national team in the 1996 Summer Olympics before entering the Japanese professional leagues.