Sato Masaki was born on May 7, 1999 in Hokkaido, Japan. Sato's given name, "Masaki", means great timber tree. It's a common masculine and less common feminine Japanese given name. When she auditioned for Morning Musume, Sato was a 6th grade elementary school student. She graduated high school in March 2018. She has two younger sisters.
Morning Musume career
2011–2012
In 2011, Masaki participated in the 10th generation auditions for Morning Musume. Throughout September, she appeared weekly on the TV show Hello Pro! Time in the segment dedicated to the auditions. On September 29, 2011, at a concert at Nippon Budokan, which was part of Morning Musume Concert Tour 2011 AkiAi Believe: Takahashi Ai SotsugyōKinen Special, it was announced that Masaki Sato passed the auditions alongside 3 other girls: Haruna Iikubo, Ayumi Ishida, and Haruka Kudo. On January 11, 2012, Nippon Television started broadcasting the TV weekly drama Sūgaku Joshi Gakuen with Masaki Sato in the role of Rion Miyamasu. The TV series became her acting debut. On April 18, it was announced that Tanaka Reina and the 9th & 10th Generation members would participate in a new stage play titled Stacey's Shoujo Saisatsu Kageki. The musical ran from June 6–12. During the last few days of her first concert tour, she cut her hair short. On May 13, information was released about an event for the 9th and 10th generation members of Morning Musume as well as S/mileage's 2nd generation members, titled Mosuma FC Event ~Gachi☆Kira~. It took place on June 15, 18 and 20 at Yokohama Blitz. On October 10, it was announced that Sato would be a member of the new unit Harvest alongside Ikuta Erina, Ishida Ayumi, and Takeuchi Akari.
2013–2015
On January 11, 2013, it was released that Sato Masaki, who has been resting since December 31 due to a high fever, has been diagnosed with left neck cervical lymphadenitis after a detailed examination. She was absent for all events between December 31 through January 17. On May 7, Sato had her birthday event, titled Sato Masaki Birthday Event ~14 sai nau nauuuu!!~. Guest included fellow 10th generation member Kudo Haruka. On July 23, it was announced that Sato would be a member of the new unit Jurin alongside Juice=Juice member Miyamoto Karin. On March 13, 2014, it was announced that Sato would be a member of a newly formed SATOYAMA movement unit called Sato no Akari. On May 7, 2014, Sato celebrated her 15th birthday. This special event was called Morning Musume '14 ~Sato Masaki Birthday Event 2014~. It featured two performances in Tokyo. On May 7, 2015, Sato celebrated her 16th birthday at a special event called Morning Musume '15 Sato Masaki Birthday Event. It featured two performances at Yamano Hall in Tokyo.
2016–present
On December 22, 2016, it was announced that Sato had injured her back and was diagnosed with acute lower back pain from a lumbar herniated disc. As a result, she missed the Morning Musume '16 x ANGERME FC Event "Gachi☆Kira Christmas Sen" on December 24, as well as the cheki and handshake events on December 25, and the CDTV Special! Toshikoshi Premier Live 2016 → 2017 on December 31. On December 28, it was announced that Sato would be missing the Hello! Project COUNTDOWN PARTY 2016 ~GOOD BYE & HELLO!~ concert, as well as the January 2 to 4 shows of the Hello! Project 2017 WINTER tour due to her back injury. She would have an appointment with her doctor on January 4 to determine whether she is fit to perform again or not. On January 6, 2017, it was announced that Sato would be taking a break from activities until late February. Sato had a re-examination of her lumbar disc herniation two days before, which the doctor concluded she was still not in the condition to resume performing on stage. At the time, the UP-FRONT PROMOTION representative and Sato herself revealed that she was diagnosed with a suspected lumbar disc herniation back in June 2015, but she did not have enough time for physical training. Sato went through physical training throughout January as the doctor observed the progress of her condition. In mid-February they would judge whether she can restart activities in March. Due to being in recovery during the production period, Masaki Sato was not featured in the A-sides of Morning Musume '17's 63rd single, "BRAND NEW MORNING / Jealousy Jealousy," released on March 8. In spite of this, she was featured in Limited Edition SP's exclusive B-sides. On February 24, it was announced that Sato would be returning from hiatus on March 18, on the opening day of Morning Musume '17's spring concert tour. Her doctors stress that while she is able to slowly continue with activities, she has not fully recovered and should not push herself in risk of further injury. It was noted that UP-FRONT and Sato's family were initially apprehensive about Sato returning to work, but she assures that she knows her body best, and will continue to train in preparation for her comeback.
