[4] At the first W Series round at Hockenheim, Koyama qualified 17th and finished 7th after setting the fastest lap of the race.

[5] During the remainder of the season, Koyama earned three more points finishes en route to 7th in the championship, and was named as a returning competitor for the 2020 W Series.

[citation needed] On 7 February 2023, Koyama was announced as the third driver for Anest Iwata Racing with Arnage in the 2023 Super GT Series.

[9][10] Koyama returned to the series as the reserve driver in R'Qs Motor Sports Mercedes-AMG GT3 Evo for 2024, twinning this with full-time participation in apr's Lexus RC F GT3 in Super Taikyu.

[13] Koyama joined the Lamborghini Super Trofeo Asia season for 2024 with Iron Lynx Theodore Racing, competing with Hon Chio Leong.