In 2013 - 2016 season, Masago played in informal matches against Shikoku Island League Plus's teams and amateur baseball teams, and played in the Western League of NPB's minor leagues. On November 28, 2016, He was honored for the Western League Big Hope Award at the NPB AWARDS 2016.[2]
In 2018 season, Masago played only one games in the Pacific League.
In 2019 season, Masago played 12 games in the Pacific League. And he recorded a 26 stolen bases in the Western League and he was honored with the 2019 Western League Most Stolen base Leader Award at the NPB AWARD 2019.[5]
In 2020 season, Masago finished the regular season in 50 games with a batting average of .314, one home runs and a RBI of 6. Masago was selected as the Japan Series roster in the 2020 Japan Series. And he recorded his first hit in the Japan Series.[6]
2021–2022 season
In 2021 season, Masago finished the season with a .254 batting average, a one home run, and eight RBI in a career-high 71 games.[7]
In 2022 season, he had a .301 batting average and eight home runs in the Western League, but in the Pacific League he slumped to a .071 batting average in 29 games.[8] October 17, 2022, the Hawks announced he was a free agent.[9]