is a Japanese singer, actress and a former member of the idol group AKB48, belonging to Team A. She had a recurring role on Kamen Rider W as Elizabeth, alongside group member Tomomi Itano. Together, they make up the sub-unit Queen & Elizabeth.
On November 10, 2012, it was announced she would be making her solo debut. On November 25, Kasai performed her solo song for the first time, the title announced as . It was released on December 26. On December 17, Kasai announced that she would leave the group. Her farewell ceremony was on May 3, 2013.
She is the younger sister of former singer Rion Kasai.
On May 15, 2021, Kasai announced her marriage to acrobat gymnast and actor Keita Koyama. She gave birth to their first child, a daughter in 2022.