Tournament hosts Japan qualified for the knockout stages for the first time in their history, Sunday's hard-fought victory over Scotland also seeing them finish top of Pool A.
The 28-21 result means the Brave Blossoms next face South Africa, who were second in Pool B, rather than New Zealand, with the two-time reigning champions instead going up against Ireland.
Pleased to avoid one of the in-form teams still left standing, Hansen praised the way Japan's players had lifted their nation after the devastation caused by Typhoon Hagibis.
"Without a doubt they'd have to be considered like they are playing and performing like a Tier One nation," the All Blacks head coach told the media.
"They're now in the top eight in the world on performance and they're playing quality rugby, so I think Japan should be very, very proud of them.
"What a marvellous thing for the tournament, you know they've given the game a boost I think, they've given Japan Rugby a boost, and they've given the Japan people a boost after what was a pretty horrific weekend.
"People have said, 'Who do you want to play?' Well, they're the on-form team, so I'm quite happy they're on the other side of the draw."
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New Zealand hardly have it easy in the last eight, though, as they go up against opponents who topped the world rankings prior to the World Cup.
Ireland have also won two of the three previous meetings between the teams, including a 16-9 triumph in Dublin when they met in November 2018.
"Obviously we're facing Ireland so we know that, that's the best part, we know who we're playing," Hansen said. "They're a quality side, they've been number one this year.
"I think their last three results are loss-win-loss [for New Zealand] - there won't be any complacency in their camp, so it's pretty exciting. We're right where we want to be.
"We enjoy playing them and that doesn't change because they've beaten us a couple of times.
"A lot of people are getting caught up in the past, it's about what's going to happen on Saturday that is going to matter, anything that's happened prior to that is irrelevant."
Photo: Hannah Peters/Getty Images Caption: All Blacks coach Steve Hansen