It wouldn't be an Irish international window without concern over Johnny Sexton's fitness. Joe Schmidt said his out-half was fine after yesterday's opening win over Scotland, but the sight of Conor Murray taking over the kicking duties from the 26th minute after the No 10 was treated for a suspected groin strain will lead to inevitable fears.
fter a pre-season disrupted by a thumb problem and an unspecified leg injury, Sexton managed 60 minutes in the final warm-up game before flying to Japan.
Scotland warned they'd send lots of treatment his way, but he largely rose above any chaos and steered the team well during the 58 minutes he was on the pitch. However, the question marks will linger over his decision to stop kicking.
It's not the first time he's ceded that particular role, but if he was fully fit and firing he'd keep the kicking tee to himself.
With a bonus point win, Ireland earned wiggle-room to manage their squad through the pool.
Although Japan will be fast, Russia big and game and Samoa uber-physical; Ireland will be confident of beating all three while rotating players.
Every time they take to the field there is risk of injury and Schmidt will have had two issues dominating his thoughts as he and his team board the bullet train to Shizuoka.
When and how to use Sexton (pictured) is a decision that could have lasting repercussions on Ireland's chances of beating South Africa in an almost inevitable quarter-final in four weeks' time.
To win, Ireland will need to be at their 2018 best - a level they came close to reaching against Scotland.
Sexton played well. However, the early charge-down and indeed his thrown intercept against Wales suggests he needs games.
With a light training session tomorrow and a full run-through on Thursday between now and Saturday's match against Japan, Schmidt may err on the side of caution and instead pitch Sexton in against the Russians before wrapping him in cotton wool for the Samoa clash.
Joey Carbery took a full part in the warm-up and needs the game, while Jack Carty was impressive off the bench once again. With Conor Murray looking back to his best, they may feel they have enough to beat Japan.
The other scenario is around Robbie Henshaw and Rob Kearney, who remain with the squad despite their hamstring and calf problems respectively. Neither man was involved in the warm-up at Yokohama, whereas Keith Earls was out with the team.
He is set to come back into the equation this week but, with Bundee Aki likely to miss the game after failing his Head Injury Assessment, the number of fit and available outside backs is tight.
"Those physical demands are right up there. It was a heavyweight contest last night," Schmidt said of the clash between New Zealand and South Africa.
"We might be light heavyweight or middleweight, I don't know, but it was a super game last night. Maybe slightly different conditions, but South Africa were bristling and the All Blacks were brilliant at times with those two tries they got.
"It's a very different situation from the World Cup last time, where we were trying to build our way through the pool knowing France was the highest-ranked opponent we were going to have and it was going to be a real mountain to climb into that game.
"We may be able to manage the squad, you might think, but Japan, that first half they played against England, they went through the Pacific Nations Cup unbeaten.
"They're a dangerous team and if they get some tempo, we might be on the back foot. We've got to take it step-by-step."
The fact that Rory Best went 80 minutes against Scotland shows that there is a plan. The captain is highly unlikely to lead his team against Japan, with Niall Scannell fresh. Peter O'Mahony is another who is likely to miss out as he, like Aki, goes through the return-to-play protocols.
Like Sexton, Schmidt said Tadhg Furlong is fine, although he received treatment before coming off.
They're all concerns, but the nature of the win gives the coach the space to make decisions on his own terms.