Hirakawa and Cassidy won the opening round of the season at Fuji Speedway, giving the new Toyota GR Supra a debut victory, and heading into the final two races of the season the pair sit within one point of championship leaders Sho Tsuboi and Kazuya Oshima.
However, Cassidy was ruled out of the chance to fight for a second SUPER GT title to go with the one he and Hirakawa earned together in 2017 due to his Formula E commitments ahead of his switch to the all-electric series with Envision Virgin Racing in 2021.
A trip to Italy for a private test at Italy’s Magione circuit last week in effect ruled Cassidy out of taking part in this weekend’s Motegi round, while the final race of the season at Fuji clashes with Formula E’s official pre-season Valencia test.
It means Hirakawa will be fighting to become the first solo champion in the GT500 class since Ryo Michigami won the title for Mugen and Honda in 2000, with reigning champion Kenta Yamashita being drafted in to take Cassidy's place.
“I’ve been with Nick for four seasons [since 2017], and it’s a shame we couldn't fight together until the end of the season,” Hirakawa told Motorsport.com.
“I have slightly mixed feelings. After all, as a professional driver and as a Toyota driver, I want to do my job properly. Yamashita is also a great driver, so I'm not worried about anything. I think I’ll soon be used to it.
“A while ago I was in touch with Nick and we discussed the set-up and various things. I think he wanted to drive too. But he is taking on new challenges and it was difficult for him to do both [SUPER GT and Formula E] at the same time, so it can’t be helped."
Ryo Hirakawa, Nick Cassidy（#37 KeePer TOM'S GR Supra）
Hirakawa and Cassidy's final race of the season together ended in disappointment as Cassidy collided with Tadasuke Makino's Kunimitsu Honda while the two cars entered the pits running nose-to-tail, giving the #37 machine terminal damage.
Kenta Yamashita (#37 KeePer TOM'S GR Supra）