Ōshima has 9 golden glove awards which is the most by any player in Chunichi Dragons history.

From middle school, Ōshima played for Tōkai Challenger in the junior boys league as both pitcher and outfielder.

After graduating university, Oshima joined Nihon Seimei in the industrial league.

In his first year he was installed as lead-off hitter and in January 2008, batted .563 in the Japanese National Championships.

[5] On August 26 2023, he hits 2000th home runs in a game with Yokohama DeNA BayStars, become a Meikyukai member.