Here, the PA news agency takes a look ahead to the action on Thursday when England play the United States and Italy meet Canada.
England sweating on next assignment
England face the first true examination of their preparations for the humidity of Japan when they clash with the USA on Thursday.
The World Cup title quest continues at the Kobe Misaki Stadium, where Eddie Jones' squad completed the eve-of-match captain's run – their first significant training session since arriving from Sapporo on Sunday.
When the Pool C showdown kicks off in the evening, the temperature will be 25 degrees with a humidity of 78 per cent.
"Ball control is an area we'll look to improve on judging by running around out there just now," scrum-half Ben Youngs said after training.
"It's pretty humid and pretty slippery. It will be a good chance to test how well we've worked on that because training has been pretty minimal this week, just walk-throughs."
Gold turns up the heat on all-star opponents
United States coach Gary Gold drew heavily on the underdog card as they prepare to launch their World Cup campaign.
Of the eight previous tournaments they have qualified for, the USA have won just three matches – in 1987, 2003 and 2011.
"We don't really have anything to lose. Expectation is quite low, nobody will give us a chance. Conversely, that puts pressure on a team like England," he said.
"We've all been there, no matter at what level you have or haven't played at or coached: you know when you're playing a team that on paper is supposed to be weaker than you."
Azzurri also expect it to be hot
Italy are bracing themselves for temperatures of 29 degrees when they take on Canada at Fukuoka Hakatanomori Stadium on Thursday.
Scrum coach Giampiero De Carli said after the captain's run: "It will be very hot; (Thursday) will be even hotter than it is (on Wednesday).
"We just have deal with this heat when we play. It is something we are used to having to deal with."
While the Azzurri opened their campaign with a bonus-point 47-22 win over Namibia, Canada are gearing up for their first run-out.
South Americans celebrate as Fiji flop
Fiji captain Dominiko Waqaniburotu admitted his side under-estimated the challenge of Uruguay as they suffered a shock 30-27 defeat at the Kamaishi Recovery Memorial Stadium.
The South American minnows, who were playing their first game of the tournament, condemned the Pacific Islanders to their second defeat in five days to leave their Pool D qualification hopes in tatters.
Waqaniburotu said: "Everything went wrong today.
"It's not the result we wanted. We under-estimated a very good Uruguay team in the first outing for them. Congratulations to them."
Fiji outscored their opponents by five tries to three but Josh Matavesi and Ben Volavola missed five out of six goal kicks between them, in sharp contrast to Uruguay fly-half Felipe Berchesi, who kicked six from seven to win the man-of-the-match award.
Hodge banned for rest of pool matches
Australia wing Reece Hodge will miss the rest of the pool matches after being given a three-match ban for his controversial tackle on Peceli Yato in the Wallabies' Pool D victory over Fiji on Saturday.
Hodge appeared to make contact with the Fijian flanker's head in a no-arms tackle in the 25th minute in Sapporo.
Yato, who scored the opening try, failed a head injury assessment and did not return to the field.
Hodge was cited for the challenge and faced an independent disciplinary committee in Tokyo on Wednesday which determined the incident was a reckless act of foul play and warranted a red card.
World Rugby's mandatory mid-range entry point, which was introduced in 2017 to mitigate the risk of head injuries, carries a minimum six-match suspension but the committee halved the penalty due to the player's exemplary disciplinary record, good character and conduct at the hearing.