Career background
Masaki advanced from Keio High School to Keio University and was selected by SoftBank in the second round in 2021. His first-team introduction in 2022 comprised 35 games and three home runs. Playing time fell to fifteen games the following year, illustrating the competition and adjustment involved in moving from university baseball to the professional level.
In 2024 he hit .270 in eighty games, supplementing seven homers with 21 doubles. His first-team appearances fell to seventeen in 2025, when he hit .259. His early professional years after university have alternated between expanded opportunities and renewed competition for a place.