さくら学院
On August 2, 2010, at the age of 11, Mizuno joined Sakura Gakuin, an idol group managed by the talent agency Amuse, Inc. She joined at the same time as another future Babymetal member, Moa Kikuchi. Sakura Gakuin had not yet released its debut single. During their audition, Mizuno and Kikuchi performed a duo dance cover of "Over The Future" by Karen Girl's, two former members of which, Ayami Mutō and Suzuka Nakamoto, had also recently joined Sakura Gakuin.