Impul Toyota driver Hirakawa started the seventh round of the season from 13th on the grid, but was already inside the points range within a handful of laps as he gained ground in the wet conditions.
But an off-track excursion at Turn 4 dropped Hirakawa back down to 12th on lap 7 of 37, before his race came to a premature end on lap 26 as he spun at the final sequence of corners and got beached in the gravel.
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Speaking post-race, Hirakawa said he thinks that he simply aquaplaned on standing water that he was unable to see properly due to the water leaking into his visor from the early stages.
"It happened on about the third or fourth lap," Hirakawa recalled. "I tore a strip from my visor, and I couldn’t see anything. Basically, it was already hard to see [through the spray] but it got even worse.
"The visor contains a heated wire to stop it from fogging up, but after a few times using it, the heat deforms the visor and creates a small gap, and then water gets inside. It meant I couldn’t see any of the rivers or standing water on the track.
"I think I spun on one of the rivers. It was quite scary while driving because I couldn’t see, so I’m glad I didn’t have a big crash."
Hirakawa's latest non-score leaves his title hopes hanging by a thread, with 40 points now separating he and third-place finisher Tomoki Nojiri.
But after another difficult qualifying session in which he was eliminated in Q1, Hirakawa says his focus is simply on regaining his mojo during Sunday's second race of the Motegi double-header weekend.
"I’m not thinking about the title now as I’m out of my rhythm, so tomorrow [Sunday] I want to do a proper attack lap in qualifying, although I doubt the position will change much," he said.
"There was no grip at the rear [in qualifying on new tyres]. Even if I had made it into Q2, I don’t think I would have started that much higher on the grid. But on Friday [in free practice] we were in good shape, so we'll compare the data from that day and do our best to come back."
Fenestraz didn't want to risk P2
Hirakawa's place as Nojiri's nearest challenger in the drivers' standings has been taken over by Sacha Fenestraz, who started and finished second behind race winner Naoki Yamamoto.
Kondo Racing man Fenestraz now trails by 30 points with three races remaining after finishing one place ahead of Nojiri.
Reporting similar visor issues to Hirakawa, Fenestraz decided against risking everything to try and pass Yamamoto and said he was pleased to narrow the gap to championship leader Nojiri.
"There wasn’t a lot of action, I just stayed in P2 for the whole race, but on lap 10 I lost about three seconds as I locked up and went off on the grass," reflected Fenestraz. "I was very close to going in the gravel, so I was a little bit lucky there.
"I couldn’t see anything when I was close to Naoki. Hirakawa had the same problem, but there was a lot of water getting inside the visor and we couldn’t see anything. I just tried to stay calm, stay on track and score those important points for the championship.
"I was pushing a lot to win, even after the safety car restart, but then I thought I shouldn’t take too much risk."
