The iconic Calsonic-liveried #12 machine, the only one of the four new Nissan Zs to use Bridgestone tyres, was in podium contention for most of Sunday's curtain-raiser, running as high as second with 10 laps to go.
However, Hiramine suffered a dramatic loss of pace in the closing part of the race, losing out to both the Kunimitsu Honda NSX-GT and the Cerumo Toyota GR Supra in a thrilling three-way dice at the hairpin, before surrendering further places to the two NISMO Zs and the best of the TOM'S Toyotas.
It meant that Hiramine and Baguette ended up back in the position they started, seventh, at the chequered flag, and only third among the Nissan contingent.
Hiramine was baffled by his loss of speed, having initially been able to match or even exceed the pace of the long-time leading Rookie Racing Toyota that eventually secured the victory.
"At the beginning of the stint, I was quite comfortable driving and we had the pace, after I got up into second it felt like we could even catch car #14 [Rookie Toyota] and we could fight maybe even for a win," Hiramine told Motorsport.com.
"But from the middle of the stint, I don’t know why, but our pace started getting slower and slower. We are waiting to be able to analyse the data and tyres. I don’t know why [we lost pace].
"Anyway, the Michelin [NISMO] cars were so fast, we couldn’t expect that. Even on the last lap, they were running in the 1m21s or something… super-fast."
Hiramine's teammate Baguette was in charge of the opening stint, fighting his way up to seventh to fifth before pitting on lap 32, gaining time with an overcut strategy.
The Belgian hypothesised that the first full-course yellow, which was called on lap 68 of 82, may have been the team's undoing.
"Maybe the tyres cooled and he couldn’t get the grip back after that, and when you are in a big pack like we were, when you are being passed by a lot of cars, it’s really difficult to stop this," Baguette told Motorsport.com. "We need to analyse what happened, if it was tyre temperature, pick-up or whatever.
"We are really disappointed with P7. If you told me before the weekend we would finish P7, I would have taken it, but looking at how the race went, we can only be disappointed. We had the pace for P2."
However, Baguette was still keen to take the positives of a strong debut showing for the Z, the best of which finished third thanks to the efforts of NISMO pair Tsugio Matsuda and Ronnie Quintarelli.
"The car is fast, the Michelin [NISMO] cars were flying at the end, so it shows the Z has a lot of potential," he said. "I think it’s not the best circuit for the Z as well, we should be stronger in other places.
"I have been really impressed by the team this weekend. The strategy was spot on, Kazuki did an amazing job as well. We need to understand what happened in the last 10 laps, but I’m really happy about what I saw this weekend, and I’m looking forward to the next race."
Hiramine was similarly upbeat about Impul's chances of fighting at the head of the field in the next race at Fuji in May.
"It feels like we can fight," he said. "Compared to last year the performance is improved, so that’s positive. Now we are looking forward to fighting again at Fuji. We’ll try the maximum [to win]."
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