At the 2018 Rhythmic Challenge in February, Mizuno was third all-around with a score of 63.800. At the end of March, Mizuno was assigned to four international competitions: Sofia International Tournament from March 30-April 1; Baku World Cup in Baku, Azerbaijan from April 27-29; Guadalajara World Challenge Cup from May 4-6; and Portimao World Challenge Cup in Portimao, Portugal from May 11-13. In July at the US Gymnastics Championships, Mizuno was fourth in clubs and fifth all-around. At the Pan American Championships in September, she won silver in hoop, behind teammate Laura Zeng and ahead of Mexico's Marina Malpica.