How big was this result ... let me put in proper perspective ... if it was the football World Cup, is it like Malaysia beating Brazil ... ono because Malaysia cannot even make the World Cup finals proper.
So, this is also NOT like Japan beating Brazil in the World Cup because Japan is a proper force in football and its not that shocking even if Japan beats Brazil. This is like New Zealand beating Germany in the World Cup.... cause South Africa or the Springboks had been multiple champions in their past lives, and NZ like Japan has never ever come close to football glory and rugby glory respectively.
Even that comparison is not sufficient because its harder for underdogs to usurp their higher ranked foes in rugby than say football. In football, you can get a lucky goal, a deflected free kick, a mistake ... and then defend like hell and still beat a higher ranked opponent. In rugby, its muscles and grind and pressure constantly, you get very few freebies, you need muscle and deft passes and great tackling to get yardage. Which is why Japan is over the moon with the victory, they literally played out of their skins, and when the opportunity to tie presented itself a couple of times in the dying minutes, they did not take it but went for victory instead.