Under her solo project Rei, ex.E-girls member Washio Reina will digitally release a new song titled "Hoseki feat. Ikuta Lilas" on November 17.

Featuring Ikuta Lilas, also known as ikura from YOASOBI, "Hoseki feat. Ikuta Lilas" is Rei's first collaboration song. Rei is a listener of both YOASOBI and Ikuta, and has uploaded a cover video of Ikuta's "Answer" on her YouTube channel. Moreover, when Ikuta was a middle school student, she used to be in charge of Rei's parts when she and her friends danced to E-girls's songs. All of this led to this collaboration. "Hoseki" was written by Ikuta, and it's her first time providing a song to another artist. 

Rei commented, "Although the theme is a new departure, you can feel people's weakness such as conflict and loneliness. It's a support song for people trying to move forward, a warm song that will gently nestle beside you."