So, after their famous victory over South Africa at the 2015 tournament, Japan have claimed another mighty scalp by beating Ireland in the 2019 edition that they are hosting.
The victory throws Pool A wide open.
Japan, who play Scotland in their final groups game have two wins from two matches, with both the Scots and Irish now with one defeat on their record.
Bonus points could come into play to decide the final standings with New Zealand and South Africa likely to face whichever teams progress in the final eight.
The result will be a massive filip for the tournament though with the hosts now with a very real chance of making the last-eight target they set out before it's start.
You can catch up with Michael Morrow's report from Shizuoka over here and we will have all the best reaction from a seismic result on the BBC Sport website and app.
Big in Japan
FT: Japan 19-12 Ireland
.Copyright: .
The Brave Blossoms are leading the Japanese news websites
Japan have recorded their first ever victory against Ireland in Test
rugby, they’d lost each of their previous seven by an average margin of 31
points.
Three of Ireland’s last four pool stage defeats at the Rugby World Cup
have come against the host nation, also losing to Australia in 2003 and France
in 2007 (also v Argentina in 2007).
Japan have won five of their last six matches at the Rugby World Cup, this
after winning just one of their initial 24 matches at the tournament (D2, 21).
Ireland have lost to a non-Tier 1 nation at the Rugby World Cup for the
first time, they’d won each of their previous 15 such games.
'We knew how tough it would be'
FT: Japan 19-12 Ireland
Getty ImagesCopyright: Getty Images
Ireland hooker Rory Best on BBC Radio 5 Live: "We knew how tough it was going to be, anyone who is utterly shock hasn't seen how good they were. We had a game plan and were prepared, we made a few mistakes and were on the wrong side of the penalty count.
"But Japan played really well and posed us a lot of questions, unfortunately we couldn't come up with the right answers.
"When you play the host team it's always tough, we didn't start how we wanted and we let them play, sometimes we were chasing shadows. You have to give credit to Japan, they attacked us minute after minute.
"We have to dust ourselves down and get better."
'We backed ourselves'
FT: Japan 19-12 Ireland
ReutersCopyright: Reuters
Japan's Pieter Labuschagne on BBC Radio 5 Live: "We are really happy, it is difficult to put it into words, just proud of every boy. That was a great game (against South Africa), but we came into this tournament with a new goal and knew what we wanted to do. We backed ourselves going into this game.
"I just want to thank each and everyone for coming out to support us, you were amazing."
Post update
FT: Japan 19-12 Ireland
BBC Radio 5 Live
More from Joe Schmidt, on 5 Live: "Congratulations to Japan, what a furious and intense effort it was. We knew it was potentially coming. They are a tremendous side and did really well."
Gratitude and glory
FT: Japan 19-12 Ireland
GettyCopyright: Getty
Michael Leitch leads the Japan team in thanking the Shizuoka crowd.
Ireland coach Joe Schmidt told ITV: "I felt we played well in the first quarter, we got into a 12-3 lead and then stopped playing. We probably fell on the wrong side of the penalty count. Three or four of them were for offsides that we felt were pretty tough.
"It just gave them the front foot and they didn't button off. Congratulations to Japan, what an intense effort that was. We knew that was coming but we are disappointed we didn't manage to control the end of the game."
'This wasn't a fluke'
FT: Japan 19-12 Ireland
Shane Horgan
Former Ireland wing on BBC Radio 5 Live
GettyCopyright: Getty
This tournament needed a second-tier nation to beat a first-tier nation and this was no fluke.- they thoroughly deserved it, out-played Ireland - all of a sudden this tournament becomes very, very tricky for Ireland.
The approach to the game was wrong, quite naive. We looked one-dimensional, kept going one or two metres outside the ruck on each attack and that's exactly where the Japanese wanted us to go. Our kicking game wasn't very good, we should have made a change at nine earlier.
'Difficult to put into words'
FT: Japan 19-12 Ireland
Getty ImagesCopyright: Getty Images
Speaking to ITV, Japan stand-in captain Pieter Labuschagne said: "We are really happy. It is difficult top put it into words but I'm
proud of every man and it was a great team effort. That [South Africa 2015] was a great game but we came into this tournament with
a new goal.
"We knew what we wanted to do and we backed ourselves. I just want
to thank everyone for taking time to come and support us. They were amazing."
'Ireland had no game'
FT: Japan 19-12 Ireland
Dennis Hickie
Former Irish wing Denis Hickie on BBC Radio 5 Live
Getty ImagesCopyright: Getty Images
Ireland didn't score a point in the second half and didn't look like scoring a point, the chances they had to put any sort of pressure on Japan they didn't take, they had no game in the second half at all.
Japan grew into the game but didn't ask huge questions, but asked enough to be the better side in the second half by some distance.
Post update
FT: Japan 19-12 Ireland
Ben Ryan
Fiji's Olympic Sevens gold medal-winning coach on BBC Radio 5 Live
Seismic, what an amazing game of rugby. So much positive we can take from this. This was textbook from Japan, any young kids watching who want to see how to tackle properly should watch this Japan team.
Live Reporting
Mike Henson
All times stated are UK
AFPCopyright: AFP 
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GettyCopyright: Getty -
Japan have recorded their first ever victory against Ireland in Test
rugby, they’d lost each of their previous seven by an average margin of 31
points.
-
Three of Ireland’s last four pool stage defeats at the Rugby World Cup
have come against the host nation, also losing to Australia in 2003 and France
in 2007 (also v Argentina in 2007).
-
Japan have won five of their last six matches at the Rugby World Cup, this
after winning just one of their initial 24 matches at the tournament (D2, 21).
-
Ireland have lost to a non-Tier 1 nation at the Rugby World Cup for the
first time, they’d won each of their previous 15 such games.
Getty ImagesCopyright: Getty Images 
ReutersCopyright: Reuters 
GettyCopyright: Getty 
GettyCopyright: Getty View more on twitterView more on twitter 
ShutterstockCopyright: Shutterstock View more on twitterView more on twitter 
GettyCopyright: Getty 
GettyCopyright: Getty 
Getty ImagesCopyright: Getty Images 
Getty ImagesCopyright: Getty Images 
View more on twitterView more on twitter 
Latest PostA result for the ages
FT: Japan 19-12 Ireland
So, after their famous victory over South Africa at the 2015 tournament, Japan have claimed another mighty scalp by beating Ireland in the 2019 edition that they are hosting.
The victory throws Pool A wide open.
Japan, who play Scotland in their final groups game have two wins from two matches, with both the Scots and Irish now with one defeat on their record.
Bonus points could come into play to decide the final standings with New Zealand and South Africa likely to face whichever teams progress in the final eight.
The result will be a massive filip for the tournament though with the hosts now with a very real chance of making the last-eight target they set out before it's start.
You can catch up with Michael Morrow's report from Shizuoka over here and we will have all the best reaction from a seismic result on the BBC Sport website and app.
Big in Japan
FT: Japan 19-12 Ireland
The Brave Blossoms are leading the Japanese news websites
Post update
Post update
Japan break new ground
FT: Japan 19-12 Ireland
'We knew how tough it would be'
FT: Japan 19-12 Ireland
Ireland hooker Rory Best on BBC Radio 5 Live: "We knew how tough it was going to be, anyone who is utterly shock hasn't seen how good they were. We had a game plan and were prepared, we made a few mistakes and were on the wrong side of the penalty count.
"But Japan played really well and posed us a lot of questions, unfortunately we couldn't come up with the right answers.
"When you play the host team it's always tough, we didn't start how we wanted and we let them play, sometimes we were chasing shadows. You have to give credit to Japan, they attacked us minute after minute.
"We have to dust ourselves down and get better."
'We backed ourselves'
FT: Japan 19-12 Ireland
Japan's Pieter Labuschagne on BBC Radio 5 Live: "We are really happy, it is difficult to put it into words, just proud of every boy. That was a great game (against South Africa), but we came into this tournament with a new goal and knew what we wanted to do. We backed ourselves going into this game.
"I just want to thank each and everyone for coming out to support us, you were amazing."
Post update
FT: Japan 19-12 Ireland
BBC Radio 5 Live
More from Joe Schmidt, on 5 Live: "Congratulations to Japan, what a furious and intense effort it was. We knew it was potentially coming. They are a tremendous side and did really well."
Gratitude and glory
FT: Japan 19-12 Ireland
Michael Leitch leads the Japan team in thanking the Shizuoka crowd.
They were truly the 16th/24th man.
Shocked in Shizuoka
FT: Japan 19-12 Ireland
Match stats
FT: Japan 19-12 Ireland
Japan-Ireland
Possession: 51%-49%
Territory: 48%-52%
Metres run: 471-318
Clean breaks: 5-7
Defenders beaten: 20-13
Turnovers conceded: 13-15
Tackles made/attempted: 158/171-127/147
Penalties conceded: 6-9
Post update
'Japan didn't button off'
FT: Japan 19-12 Ireland
Ireland coach Joe Schmidt told ITV: "I felt we played well in the first quarter, we got into a 12-3 lead and then stopped playing. We probably fell on the wrong side of the penalty count. Three or four of them were for offsides that we felt were pretty tough.
"It just gave them the front foot and they didn't button off. Congratulations to Japan, what an intense effort that was. We knew that was coming but we are disappointed we didn't manage to control the end of the game."
'This wasn't a fluke'
FT: Japan 19-12 Ireland
Shane Horgan
Former Ireland wing on BBC Radio 5 Live
This tournament needed a second-tier nation to beat a first-tier nation and this was no fluke.- they thoroughly deserved it, out-played Ireland - all of a sudden this tournament becomes very, very tricky for Ireland.
The approach to the game was wrong, quite naive. We looked one-dimensional, kept going one or two metres outside the ruck on each attack and that's exactly where the Japanese wanted us to go. Our kicking game wasn't very good, we should have made a change at nine earlier.
'Difficult to put into words'
FT: Japan 19-12 Ireland
Speaking to ITV, Japan stand-in captain Pieter Labuschagne said: "We are really happy. It is difficult top put it into words but I'm proud of every man and it was a great team effort. That [South Africa 2015] was a great game but we came into this tournament with a new goal.
"We knew what we wanted to do and we backed ourselves. I just want to thank everyone for taking time to come and support us. They were amazing."
'Ireland had no game'
FT: Japan 19-12 Ireland
Dennis Hickie
Former Irish wing Denis Hickie on BBC Radio 5 Live
Ireland didn't score a point in the second half and didn't look like scoring a point, the chances they had to put any sort of pressure on Japan they didn't take, they had no game in the second half at all.
Japan grew into the game but didn't ask huge questions, but asked enough to be the better side in the second half by some distance.
Post update
FT: Japan 19-12 Ireland
Ben Ryan
Fiji's Olympic Sevens gold medal-winning coach on BBC Radio 5 Live
Seismic, what an amazing game of rugby. So much positive we can take from this. This was textbook from Japan, any young kids watching who want to see how to tackle properly should watch this Japan team.
Post update
Post update
FT: Japan 19-12 Ireland
Becky Grey
BBC Sport at Kobe fan zone
Anyone who questioned whether Japanese people like rugby before this World Cup need only spend five minutes in the Kobe fan zone to get their answer.
Absolute scenes, as they say. People screaming, jumping up and down, all the things you’d expect when your side has just caused a massive upset.
Post update
FT: Japan 19-12 Ireland
Dennis Hickie
Former Irish wing Denis Hickie on BBC Radio 5 Live
Ireland have ceded control to the other teams in their group and all the mistakes from the warm up have come back to haunt them.
Remember the runners-up from this Pool will most likely face the All Blacks in the last eight.
The runners-up will probably face the Springboks. Which might be the marginally easier route to the final.
Of course, Ireland might not fill either slot.