Mari Yaguchi
In 2003, Shimizu was chosen to join the group ZYX, which consisted of five Hello! Project Kids and Mari Yaguchi, who acted as a mentor. They released two singles: "Iku ZYX! Fly High" and "Shiroi Tokyo". They remained active until 2004, when Saki and Momoko Tsugunaga became members of Berryz Kobo.