Oita - Japan have blossomed from charming hosts to pool pacesetters with their victory over Ireland at the Rugby World Cup, with even All Blacks coach Steve Hansen finding plenty to learn from the Asian giantkillers.

"We'd be very silly if we didn't, because they did plenty to give us something to think about," Hansen said on Monday when discussing potential quarter-final opponents.

"Their speed of ball was great, their line speed was awesome, they just kept coming, time after time after time (and) showed a lot of courage, intent and a lot of skill."

Having backed up their 2015 victory over South Africa with another colossal upset, the Japanese again find themselves closing in on a berth in the last eight.

Unlike in 2015 when a lack of bonus points cost them after finishing equal with South Africa and Scotland on three wins from four pool games, this time they have already banked a vital bonus point - in the World Cup curtain-raiser against Russia.

With only Samoa and Scotland left to play, one more win could put the Brave Blossoms in line to potentially play either New Zealand or South Africa in the quarter-finals - which has got Hansen's attention.

"If we have to play Japan then we will prepare accordingly and we'll expect what we saw the other day - them coming at us at 100 miles an hour and wanting to turn opportunities into fast ball," he said.

"We'll have plans to make sure they can't do that and, no different to any other game, we'll have strategies to try and combat what they do, what their strengths are, and try and attack their weaknesses."

Japan coach Jamie Joseph, a New Zealander whom Hansen rates as good enough to coach the All Blacks, has drawn criticism from some quarters for including 16 overseas-born players to compensate for the Japanese lack of size and physicality.

It's given rise to the term "glocal" within the squad - a mix of global and local.

Most qualify under the three-year residency rule - the same way Joseph was able to play for Japan at the 1999 World Cup after playing for the All Blacks in the 1995 final - and he maintained individual nationalities do not feature within his squad.

"We call it 'One Team' because it takes everybody in that squad to get a performance like that. It is the team culture that gets us over the line," he said after the win against Ireland.

"Our team wants to make the top eight. The last World Cup Japan did very, very well but still didn't make the top eight so that's been the target all along, that's our team goal."

It may come down to their final Pool A match against Scotland in two weeks and Australian-born lock James Moore said the heartache of four years ago will be a driving force.

"Everyone is thinking about that, so I guess bonus points are important and we have to focus on winning our matches and getting our preparation right."

Japan's only loss in 2015 was when they went down 45-10 to Scotland.