But her time at the wheel of the Arnage Racing Lexus RC F GT3 she shares with Igor Fraga and Yuga Furutani was not one she will remember fondly, as she was forced to struggle on a drying track while using wet tyres.
Koyama took over on lap 67 of 93, just as the race was restarting after the red flag caused by the Tsuchiya Engineering Toyota GR Supra's fire, with the track still much too wet to contemplate a change to slicks.
However, the track quickly dried, with the majority of GT300 cars changing to slicks as a result, but the Arnage squad opted to keep the #50 Lexus out on wets, the team having already made three pitstops.
The result was that Koyama took the chequered flag 19th in class and a lap behind the winning Gainer Nissan.
"The track was drying out in the closing stages, and if we had pitted we would have lost a lot of positions, so we decided to stay out on wet tyres until the end," recalled Koyama, last year's Formula Regional Japanese champion.
"It’s unfortunate that it just became a race of survival, but I’m glad I was able to make it to the end."
Koyama was poised to become the first female starter in SUPER GT since Cyndie Allemann back in 2012 when she joined the Arnage team as the third driver alongside Fraga and Furutani for the 450km races on this year's schedule.
The Toyota junior was unable to run in the first two longer races of the season at Fuji and Suzuka, but the Anest Iwata-sponsored team signalled in advance of last weekend's fourth round of the season that Koyama would drive a stint.
"When I started my stint there were a lot of blue flags, I had to let a lot of cars pass me and it was difficult to settle into a rhythm," continued Koyama. "After that, I would say my pace wasn’t too bad.
"But for me personally it was frustrating that the track started to dry out. I wanted to push as it was my first race. I wanted to go on the attack. Because the track dried while I was on wet tyres, it wasn’t about being quick but just surviving.
"The team wanted me to stay out so that we could finish in the highest position possible, but I personally would have been happy to drop positions [by changing on to slicks] if it allowed me to push.
"I wanted to drive for longer, and I wanted to push. I wanted to show something positive to the many people who have been supporting me."
Two of the remaining races on this year's calendar, Round 5 at Suzuka and the penultimate event at Autopolis, will also be run over 450km, providing further opportunities for Koyama to race.
Additional reporting by Kunihiko Akai
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