Ryohei Yamanaka's first experience of World Cup rugby may have come eight years after he had initially hoped, but the 31-year-old back is relishing every minute.

"It was great to finally play. I only got a short amount of playing time but it really was a dream come true and something I really strived for," Yamanaka said Tuesday, referring to his cameo performance off the bench in Japan's Pool A opener against Russia.

Back in 2011, Yamanaka was widely tipped to make Japan's squad for the New Zealand tournament.

However, he tested positive for a steroid in a random doping check in April of that year during a training camp ahead of the Asian Five Nations.

When the follow-up test showed the same result, he was banned from the sport until April 27, 2013.

Yamanaka, who had graduated from Waseda University just a month earlier, told rugby authorities he had used a hair growth cream in an attempt to grow a mustache and that he thought the cream was a cosmetic product that did not contain any banned substances.

Having served his ban, he started playing for the Kobe Kobelco Steelers where he was transformed from a flyhalf to fullback and his good form over the last few years has seen him go on to win 14 caps.

On Saturday, he is likely to be handed a starting role as Japan goes up against Ireland in a game in which Yamanaka's strength under the ball is likely to be tested to the full.

"Ireland kick a lot so contesting and catching will be really crucial," he said. "So if I get the opportunity to play that will be my key focus."

Yamanaka showed in the Pacific Nations Cup game against the United States in August and in the 10 minutes he played against Russia that his strong left boot has now been complemented by a good running game.

As a replacement, he was keen to make an impact.

"As I had been preparing throughout the week to come off the bench, it was crucial that I could give the team some momentum," he said.

"When I came on, it was really crucial to kick well, kick to touch and also make line breaks. And I was able to add some impact and flow to the team."

If he does start, as coach Jamie Joseph rejigs his back three, he can expect a steady stream of high kicks to come his way — especially if Ireland opts to start with Conor Murray and Johnny Sexton at halfback, though reports from the Irish camp Tuesday hinted the latter may miss the game with a quad injury.

The Brave Blossoms struggled under the up-and-unders both against South Africa in their final warm-up game and against the Russians, and Murray and Sexton are masters of the art.

"There are different situations in the kicking game," said Yamanaka. "It could be a box kick, a high ball from 10, so we're simulating those different scenarios. We are trying to make sure we work well under pressure."

Pressure is also expected to be exerted on the Japan pack at scrum time. But forwards coach Shin Hasegawa seemed confident his side is ready for the challenge, even though a second-string Ireland side comfortably beat Japan in a two-test series in 2017.

"We need to nullify their strong loosehead and tighthead, so we don't let them scrum at 100 percent," Hasegawa said. "We feel confident in our scrum. We just need to be determined and committed."

Joseph is set to name his 23-man squad on Thursday, two days before the Brave Blossoms face Ireland at Shizuoka Stadium Ecopa.