Japan and South Korea have made massive progress in recent years. Football is becoming increasingly popular there, and with their impeccable work ethic, organization, etc., they will both be very big teams in the future. Exciting progress and great news for football in general.
Hungary beat England 0:4 at Wembley in the last year or so. Japan would have a decent chance against England. Obviously, 0:4 or 1:4 is a bit of a freak result, but it's not beyond the realms of possibility. Hungary did it to England, and Japan did it to Germany. It could happen. Neither were favourites. Speaking of which, Hungary is another significantly improved team, especially in the last few years. Wins away against Germany, England, and Serbia, draw against France, and more.