Leon Masuda was born in Tokyo, Japan. Her mother is a model and former Miss Japan 1999. Leon is an only child and lives with her single mother. She is fluent in Japanese/English.
Leon started modeling and acting as an infant. As a child actor, she has worked steadily in television shows, music videos, fashion shows, commercials, magazines, and other events. In 2014, her talents and outgoing personality saw her star as the lead actress in the film An American Piano (2014) alongside co-stars Adam J. Yeend, Qyoko Kudo, Jun Matsuo and Lou Ohshiba.
In 2016, Leon moved to Beverly Hills, California, to pursue her dream as a Hollywood actress. Leon's first job on the big screen was in the Disney feature film, Magic Camp (2020) as a member of Team Diamond.
When she was in high school, she founded and became the President of an Anime Club. This was the first time Anime Club was founded since the opening of Beverly Hills High School in 1927, let alone being a native Japanese. This prompted her club to officially get invited to join the Anime Club Union, formed by all the high school and college Anime Clubs in California. She reveals that she was the only girl in her club and that was very unfortunate. Her favorite anime includes Akira (1988), Anohana: The Flower We Saw That Day (2011), Attack on Titan (2013), and Code Geass (2006).
Leon graduated from Denenchofu Elementary School in Tokyo, Japan, in 2014, Horace Mann School, Beverly Hills in 2016, and Beverly Hills High School in 2020. She is currently attending the University of California, Irvine (October 2020 - Present) to study mathematics.