In April, she began working full-time with the group, which debuted with the single, "Aitakatta", in October 2006.

[citation needed] On August 24, 2012, AKB48 announced a reorganization of the teams, and appointed Oshima to be the captain of Team K.[5] On December 31, 2013, Oshima announced on Kohaku Uta Gassen that she would be leaving the group.

[6] On February 26, 2014, the last single for her as a member of AKB48 and as the center performer of that, ”Mae shika Mukanee" was released.

[8] On July 29, 2021, Oshima married actor and Scarlet co-star Kento Hayashi.

In the 2012 general election, she placed first with 108,837 votes and became the center performer in the single "Gingham Check".