At the Tashkent World Cup in Tashkent, Uzbekistan on April 19-21, she finished 17th all-around and did not advance to any apparatus finals. At the US Gymnastics Championships in July, she won ball bronze with a score of 18.800, behind Laura Zeng and Evita Griskenas. Mizuno competed at the Kazan World Challenge Cup in Kazan, Russia from August 30-September 1, placing 28th all-around. At Japan's AEON Cup in October, the American team finished eighth and Mizuno finished fifteenth all-around. Mizuno started her 2020 season in February at the Rhythmic Challenge in Lake Placid, New York. Mizuno placed fourth all-around, behind Lennox Hopkins-Williams and ahead of Elena Shinohara. She was third with ball, fourth in hoop and ribbon, and seventh in clubs. Mizuno was born in Kawasaki, Japan.