Autumn kicked in hard around Tokyo on Friday and with it came the rain - hammering down on roofs, blown in gusts against windows, sending people scurrying head-down into doorways and cafes and cabs.

A day to hunker down, a day for long and deep conversations over multiple coffees, to hold back energy for all that is to follow this weekend.

Tokyo is so vast that you should be able to lose all the thousands of rugby fans that have arrived for the two World Cup semi-finals, let alone the four teams and their twitchy, scheming coaches.

Yet all day you could see the little pockets around Shibuya, and Shinjuku, and Roppongi, talking these seismic games through, trying to burn through the hours until they finally begin.

World Cup semi-final week can feel like the stretched-out days before a Ryder Cup. Too much waiting, too much speculation.

It happens because so much is at stake. England's biggest game in 12 years, a chance not only to reach a fourth World Cup final but to bring down the sport's great totems en route.

Wales with a second semi-final in three tournaments, battered and out of shape but still more capable of pulling something miraculous from nowhere than any other contender.

All the little details and sub-plots in the story settling in layers as the days drift by. You head out to Tokyo Bay and England's hotel on the edge of Disneyland and you see George Ford and Owen Farrell, caps pulled low, walking out the tension, talking quietly.

Across town in a skyscraper in the business district, brothers Beauden and Scott Barrett at a press conference, kids from a dairy farm in Pungarehu, blinking in the bright lights of the cameras and giving each other little grins and sideways looks.

Three miles to the west, up by the new Olympic stadium, Jonathan Davies testing out his injured knee, Warren Gatland watching on in impassive conversation with Shaun Edwards.

Rassie Erasmus in a smart hotel another two miles further on, talking down Cheslin Kolbe's injury and talking up his replacement Sbu Nkosi.

In each camp there are players and coaches who recognise that this weekend could define not just their World Cups but their careers and reputations beyond.

Maro Itoje, his mum and dad in town, his dad doing the dad thing of telling him what to do and when, even though he knows his son knows much more.

Richie Mo'unga understanding that he is walking in the shadow of Dan Carter and Andrew Mehrtens and Grant Fox.

Alun Wyn Jones, four World Cups into a remarkable career, thinking once more of the words he will choose to say to his team-mates before he leads them out.

Someone will make their name this weekend. You can ignore the group stages of a World Cup if you're not a die-hard but a semi-final between the giants brings in the crowds and sticks families in front of their TVs.

Maybe it will be Kyle Sinckler, the kid from south London whose power, skills and back-story could bring a new audience to the English game.

Maybe it'll be the young bucks in the All Blacks backs, Sevu Reece and George Bridge, Jack Goodhue and Anton Lienert-Brown, late bolters compared to the grizzled superstars who carried New Zealand to their last two World Cups.

If Dan Biggar kicks and steers Wales into their first World Cup final all those little doubts and slights that have dogged him even at home will be brushed away for good.

As a supporter you hold on to the hints and precedents that this might be your team's year, because having come this far it seems cruel for it all to end so close to the summit.

Both New Zealand and South Africa will walk out in Yokohama as clear favourites. They have timed their charges well, changed personnel and tactics late in the four-year cycle and made them kick on when it counts.

You bet against the All Blacks only because the odds can be so tempting. Eighteen World Cup matches won on the spin, a coach that has won the trophy as an assistant and then again with his own team.

More points per game than any other team in this tournament, more tries, more metres made. More defenders beaten, more clean breaks, more offloads.

New Zealand have won 15 of their last 16 matches against England. England have never beaten them at a World Cup.

And so Eddie Jones' men are left with a beautiful long-range punt, a complex problem reduced to a straightforward equation: play to your absolute best and you have a chance; drop off at all in any area and prepare to be roadkill once again.

South Africa have got this far by going back to the future under Erasmus, building a side based on uncomplicated power and kicking, and just a little stardust out wide.

It is the most Springbok of Springbok teams. Eben Etzebeth and Lood de Jager could be the kid brothers of Bakkies Botha and Victor Matfield. Siya Kolisi can inspire his side like Francois Pienaar. Faf de Klerk snipes just a little like Fourie du Preez.

Wales can beat them because Gatland knows what makes each of his players tick and grasps how to make them even more than the sum of their parts.

You lose Liam Williams late on, having already lost Josh Navidi and Taulupe Faletau, and it should fatally weaken a side that does not have the same luxury of depth as its rivals.

Gatland won't let that idea settle for a moment. He will see an opposition who like to run straight and hard and know that it suits his own side more than a team who go wide and unstructured early. Three Grand Slams in 12 years, at least one more unforgettable performance still to find.

The deadpan Steve Hansen against the wise-cracking snark of Eddie Jones. Erasmus, in tune with his nation's rich rugby traditions, against a man in Gatland who arrived in Wales as an outsider and will leave as one of their own.

The rain eventually faded in Tokyo, just as the light was going from the day. All to bed early in anticipation of what Saturday and Sunday's clear skies will see.