[8] In June at the USA Gymnastics Championships, Mizuno won gold in hoops and clubs, silver in all-around and rope, and placed fourth in ball.

[12] Mizuno competed at the Pan American Championships in October, capturing silver in hoop, ball, ribbon and all-around, behind teammate Evita Griskenas.

[1] At the Pan American Championships in September, she won silver in hoop, behind teammate Laura Zeng and ahead of Mexico's Marina Malpica.

However, in autumn 2020, Mizuno was invited to train with the national senior group, which had lost a member and needed a replacement, an experience that she said was enjoyable and invigorating.

[4] In 2021, Mizuno competed as a member of the United States senior group, winning both the 2021 Rhythmic Challenge and 2021 USA Gymnastics Championships.

She was selected to represent the United States at the 2020 Summer Olympics alongside Camilla Feeley, Isabelle Connor, Nicole Sladkov, and Elizaveta Pletneva.

[30] Her first international competition of the year was Marbella Grand Prix in March, where she finished fifth with hoop, sixth in all-around and clubs, and seventh with ball and ribbon.

[35] In June, she competed at the USA Gymnastics Championships, winning silver in all-around, behind Evita Griskenas and ahead of Erica Foster.

[42] The Aphrodite Cup in March was Mizuno's first international competition of the season - she was fourth in the all-around and picked up a bronze medal in ball, and she was fifth in ribbon and eighth with hoop.

[44] She returned to competition in June at the 2023 Pharaoh's Cup in Cairo, Egypt, winning four medals: gold in ball and ribbon, and silver for hoop and clubs.

[46] In July at the Cluj-Napoca World Challenge Cup in Romania, Mizuno finished 13th all-around and additionally placed fifth in ball and eighth in hoop.

[51] Competing at the 2023 Pan American Games, Mizuno finished fourth in the ribbon final, behind bronze medalist Evita Griskenas.