Oshima passed AKB48's 13th generation auditions on 9 September 2011. Her debut was on 8 December 2011 at AKB48's 6th anniversary stage performance. In August 2012, she was promoted to Team A. She started activities as a Team A member in November 2012. In February 2014, during the AKB48 Group Shuffle, it was announced Oshima would be transferred to Team B.
In the group's general elections in 2014, Oshima ranked for the first time at 80th position.[1] Her first senbatsu single was Kibouteki Refrain, and she was the first 13th generation member to be selected for senbatsu.
On March 23, 2017 during AKB48 Team B's concert, it was announced that Ryoka would graduate from AKB48 soon.[5] On 8 June 2017, Oshima graduated from AKB48.
Sang on "Kimi wo Kimi wo Kimi wo..." as Jisedai Senbatsu, "Madonna no Sentaku" as Renacchi's Sousenkyo Senbatsu, and "Kin no Hane wo Motsu Hito yo" as Team B.
Appearances
Stage units
AKB48 Kenkyuusei Stage "RESET"
"Kokoro no Hashi no Sofa" (心の端のソフャー)
Team A Waiting Stage
"Skirt, Hirari" (スカート、ひらり)
"Tenshi no Shippo" (天使のしっぽ)
"Tsundere!" (ツンデレ!)
AKB48 Team B 3rd Stage "Pajama Drive" (パジャマドライブ) (Revival)