SHIZUOKA, 25 Sep - The manner in which the Irish forwards dominated their Scottish counterparts on Sunday highlighted the challenge Japan's pack will face on Saturday - but the Brave Blossoms' backs know they also have a big job on their hands.
With one of the tournament favourites up next, scrum-half Yutaka Nagare (pictured) knows he needs to shift focus to the technical side of the game now the tricky opener against Russia has been safely negotiated.
"Ireland don't make mistakes. They are very resilient, have the ability to keep the ball and are focused when in defence," said Nagare, one of the host team's on-field leaders against the Bears.
"It's just important we have speed in our game, which will create opportunities. We need to attack that space when it presents and use possession well."
One of three scrum-halves in the Japan squad, alongside Kaito Shigeno and veteran Fumiaki Tanaka, Nagare knows his opposite number, and another of the half-backs, need the utmost attention.
"The nine (Conor Murray) and 10 (Johnny Sexton) are key players," he said. "If we let those two players play comfortably they will really come into the game and dominate.
"So it's important we pressure them at source every opportunity we get. And apply that pressure for the whole 80 minutes, especially apply immense pressure early on, so that they feel really uncomfortable from the start."
A man who could be on the receiving end of Ireland's up-and-unders is full-back Ryohei Yamanaka, who, on his World Cup debut, came on in the late stages against Russia and made a great drive as well as kicking accurately into touch on his World Cup debut.
"I only got a short game-time but it was really my dream come true, something I really strived for," said Yamanaka, who could have made his debut eight years ago had he not used hair-growth cream to grow a moustache. The cream contained banned substances and led to two-year suspension.
Japan's vulnerability when facing kicks was not so apparent in the Pacific Nations Cup against the likes of Fiji and Tonga, but it was a different story against South Africa pre-tournament. And Russia's early try in Tokyo came as William Tupou dropped a high ball, so Ireland will likely employ their beloved kicking game, which has often proved so effective against the hosts.
"There are different situations in the kicking game - could be a box kick, high ball from 10 - so we're simulating those different scenarios," Yamanaka said. "We always focus on protecting (the receiver) but we just needed more focus on that, so it's all about escorting.
"They kick a lot, so I must catch, be secure and keep possession. And it's also all about playing our game."