佐藤優樹 (Sato Masaki) is a Japanese pop singer. She is a former idol under Hello! Project as a 10th generation member of Morning Musume., as well a former member of the SATOYAMA movement units Harvest, Jurin, and Sato no Akari. She graduated from both Morning Musume. and Hello! Project on December 13, 2021 due to health issues. As of April 2022, she is part of the M-line club.