If there's a battle within the battle that could decide the All Blacks semifinal against England this weekend, it's the loose forwards.
Naturally the breakdown is a focal point every week but the form of England's twin openside flankers, dubbed the Kamikaze Kids by Eddie Jones, will have the AllBlacks on high alert.
While England's sizeable No 8 Billy Vunipola is a strength and potential weakness, Tom Curry and Sam Underhill have been a revelation since Jones thrust them together this year. Their combination has not been lost on All Blacks opposite Sam Cane.
"Underhill and Curry have been pretty impressive," Cane said as the All Blacks warmed into their penultimate week in Japan. "They've both got a huge appetite for hard work, they've got very good skillsets."
Last week in Oita, as England dumped Australia out of the World Cup with their 40-16 quarterfinal victory, Curry was named man of the match after an influential display.
The 21-year-old delivered the final pass for Jonny May's opening try and made 16 tackles – one of which almost split Wallabies utility Reece Hodge in half such was the perfect timing of the tackle.
After that hit, who was the first man swooping in for the turnover but partner in crime Underhill.
This is but one instance in which the pair clinically combined to outclass Australia's "Pooper" combination, that of captain Michael Hooper and David Pocock.
The All Blacks, of course, this year harnessed their own dual openside combination of Cane and Ardie Savea.
This double openside employment is a growing modern trend, to the point some have questioned the future of the more traditional blindside flankers.
"I'm not sure why it's come about exactly," Cane said. "It probably shows the way the game has evolved slightly where the flanker roles don't differ too much.
"It depends on a coach and what make up he wants from his loose forwards. Teams are so structured so the best chance to attack from unstructured is from turnover ball so you might increase your chances ever so slightly by having two."
To beat England, on any occasion, opposition must first match their physicality. Every aspect of their game stems from dominating collisions. Don't meet them head on there, and their pack will rumble forward and allow Curry and Underhill to make a mess of the All Blacks ruck ball.
England don't want to play at pace. They will do everything within their power to slow and stifle the All Blacks at the source by targeting the breakdown and attempting to rattle Aaron Smith.
Throw All Blacks captain Kieran Read in mix with Cane and Savea, and the challenge of colliding with Vunipola, Curry and Underhill is one they are sure to relish.
Much like Curry and Underhill, Cane and Savea's partnership with Read only evolved this year, in large part due to Liam Squire's unavailability. The success of this trio has since been obvious but Cane, feeling fresher than most after being replaced at half time against Ireland, believes there is more to come in Yokohama.
"I'd love to think we've got room for improvement, absolutely. Ardie has been working really hard on some of his set piece work which a six is required to do a little bit more. But, bar the set piece, our roles are pretty interchangeable whether that's attack or defence."
The contrasting strengths of Cane, one of the world's best defenders, and Savea, lethal with ball in hand on the edge, complements the All Blacks' back-row. This allows Read and Brodie Retallick to dominate the middle of the park.
The rapid success of the All Blacks new-look loose forwards hasn't happened by chance, and they will again need to be at their best this weekend.
"When I think about all the hard work we've put in at training, all the little catch-ups we have to make sure we're singing off the same song sheet, not really," Cane said when asked if he was surprised at how quickly he and Savea had gelled. "Ardie is a special player in his own right with a pretty special skillset which we've seen in all three loose forward positions in the All Black jersey."