Koyama came into this weekend’s penultimate round at Fuji with a healthy points buffer over her nearest rival Sota Ogawa, and extended that by finishing second behind poleman Riki Okusa in Saturday morning’s opening race of the weekend.
The second race on Saturday afternoon didn’t start well for Koyama, who dropped from her grid slot of second to third with a poor start, but she soon regained second place from Yoshiaki Katayama before going on to challenge Okusa for the lead.
Koyama was able to pass for the lead under braking at Turn 1 before taking victory by 2.5 seconds, her seventh of the season, with Ogawa beating a fading Okusa to second.
It means Koyama now holds an unassailable 86-point lead in the drivers’ standings with only three races to go, one more at Fuji on Sunday and two more at Suzuka in December.
Koyama, 25, was named a Toyota junior driver at the start of 2022 after failing to secure a place on the W Series grid.
The Japanese driver finished seventh overall in the inaugural campaign of the all-female series in 2019, but slipped to 14th upon the championship’s return last year.
Koyama made a one-off outing in Super Formula Lights last year, and the Super Formula support category would appear to be her most likely destination in 2023 if her relationship with Toyota continues.
Another Toyota junior, Kazuto Kotaka, leads the SF Lights standings heading into this month’s season finale at Okayama.