In 2017 season, he finished the regular season with a 41 Games pitched, a 3–0 Win–loss record, a 2.70 ERA, a 3 Holds, a 33 strikeouts in 36.2 innings.
In 2018 season, he finished the regular season with a 57 Games pitched, a 2–0 Win–loss record, a 2.17 ERA, a 11 Holds, a 52 strikeouts in 54.0 innings.
On August 29, 2019, Kumon broke the NPB record for undefeated pitchers in 165 games.[3] In 2019 season, he finished the regular season with a 61 Games pitched, a 2–0 Win–loss record, a 3.96 ERA, a 17 Holds, a one Save, a 31 strikeouts in 52.1 innings.
In 2020 season, he finished the regular season with a 29 Games pitched, a 0–2 Win–loss record, a 7.88 ERA, a 8 Holds, a one Save, a 19 strikeouts in 24.0 innings.