Japan have accused Cian Healy of illegal scrummaging tactics, cranking up the tension ahead of Saturday's World Cup clash with Ireland.
Tighthead prop Yusuke Kizu could find himself directly facing down the in-form Healy in Shizuoka - but had no qualms calling out the British and Irish Lions star's set-piece technique.
Hosts Japan saw off Russia 30-10 to open the tournament on Friday night, and are now setting about finding a way to topple Joe Schmidt's men, who came into the tournament ranked number one in the world.
When asked for an appraisal of Ireland's scrummage, Kizu claimed Healy angles inwards, which would flout the regulations for props to drive square.
"Their loosehead prop steps out, so they try to attack from the side, that's my impression of their scrum," said Kizu.
"Ireland's forwards really attack close to the rucks so we need to have double collisions to stop their momentum, and we need to execute our system for us to achieve that.
"It was a positive tight-five review from the Russia game in that our defence really came up hard and we were able to force them back."
Scrum coach Shin Hasegawa has called on Japan to shut down Healy and Tadhg Furlong, for Japan to stand any chance of dominating at the set-piece.
"We need to nullify their strong loosehead and tighthead, so we don't let them scrum at 100%," said Hasegawa.
"I've loved their scrum for a long time, so we really need to think about how we counter them, and how we talk and coordinate with the players.
"It doesn't matter who we come up against each scrum is different, some opponents allow us to scrum how we want and other opponents won't allow us to do what we want.
"We feel confident in our scrum, a matter of fine-tuning, we need to be determined and committed in our scrum.
"We are worried because they are a very strong side, and the more you watch them, the more you analyse them you find out they are a quality side.
"So of course there are worries. But equally that applies to any team so it doesn't matter who we come up against.
"Whether our plan will work or not is always a worrying factor."
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Follow Ireland v Japan on Saturday (kick-off 8.15am) via the live blog on RTÉ.ie/Sport andthe NewsNowApp, watch live on RTÉ2 from 7.30am or listen to live match commentary on RTÉ Radio 1.