Sayashi was one of the winners of the Jc&Jk actress audition and got a chance to perform in Morning Musume's Fashionable stage play.

Sayashi passed Morning Musume's ninth generation auditions, along with Erina Ikuta, Kanon Suzuki, and former Hello!

[4] On July 29, 2011, Sayashi was out of events for a few weeks to rest due to ischium nerve pain on her right side.

Project duo Peaberry, along with S/mileage's Ayaka Wada, and that they would perform their original song "Cabbage Hakusho" at the Hello!

[5] After leaving Morning Musume, Sayashi went to New York and other places abroad for about two years to study dancing and English.

[9] Since July 10, Sayashi has her own column called RihoColumn (りほこら(む)) in the online magazine NewsCrunch, published by Wani Books.

[10] On September 3, Sayashi announced that she has signed to Japan Music Entertainment [ja] as a solo artist.

[11] On July 14, 2021, Sayashi's staff announced the sale of her first EP, named DAYBREAK,[12][13] which was released at August 4,[14][15] under her newly established label "Savo-r",[16] and also held a one-man live tour titled "RIHO SAYASHI 1st LIVE 2021 DAYBREAK" at Toyosu PIT, Tokyo Team Smile.