The Springboks opened their doors to the public for a training session yesterday and in amongst the backs' running moves was Felix Jones.
It helps when you have a young coach who can slot in and out whenever called upon, but Jones is not here in Japan just to make up the numbers.
That much was clear during the warm-up to last weekend's defeat against New Zealand as the former Ireland out-half was heavily involved in going through drills with different players.
The odd turn of events that has seen Jones take on a role with South Africa has certainly rattled a few cages in Ireland, including Joe Schmidt who must be wondering what kind of information his former protégé is passing on to his new employers.
Indeed, some Munster fans were disappointed to lose Jones from their coaching staff as he left as soon as his contract at the end of last season.
Others will point to Munster's stuttering attack and insist that change was needed, which is why the club acted fast and brought in Stephen Larkham to add fresh impetus.
Supporters can debate Jones' worth all they like, but it is clear that some of the biggest names in the game believe he has the makings of an excellent coach. Schmidt played a key role in Jones landing the Munster gig in the first place, while he brought him on the summer tour to Japan in 2017.
As a player, Schmidt also trusted him and regularly picked Jones in his match-day squads ahead of others who would have felt they deserved inclusion over the Dubliner.
He is still in the early stages of his coaching career, but speak to anyone about Jones' qualities and it sounds that he is very much cut from the same cloth as Schmidt. Countless hours are spent analysing footage and running joke is that the South African coaching staff want to tempt him away for a beer - just to give him a break.
Like Schmidt, Erasmus holds Jones in very high regard and that the Springboks boss created a role for him tells you all you need to know. One imagines that Erasmus has locked him away and told him to dig up as much information on Ireland as possible.
If results go to form, Ireland will meet the Boks in a mouthwatering quarter-final clash and if that scenario does unfold, it will scramble Schmidt's head.
"The way Felix came in was, our attack coach Swys de Bruin unfortunately had some health issues and on very short notice, we had to get somebody new," Erasmus explains.
"I sat down with the players and we said that we can't change our attack philosophy now but we would really like to get somebody in and help us analyse the opposition's defensive structures. We don't really need that for the southern hemisphere teams because we play them on a regular basis.
"Knowing that we would probably play Scotland or Ireland or England, I coached with Felix at Munster for almost two years, I know how good he is and I know that he puts a lot in that, even on that Italian team because we played Treviso.
"The analysis he does on individual players and defensive structures is really phenomenal.
"I know his work ethic, so I didn't have to convince him to make him think the way we think.
"He is a good friend of mine also. He has settled in really well with the boys. He is still a young guy. He relates to the guys because I think he is only two of three years older than some of them.
"He is a nice guy to have around and yes, we will tap into his brain. That will be his job."
Everyone knows it is happening but to hear Erasmus outlining how he will use Jones will annoy Schmidt.
Even in terms of the language that Ireland players use around certain calls, Jones has a lot of valuable information that could seriously damage his home country.
But this is professional sport and there is no room for sentiment - he only has to look to his new boss and the manner in which he cut short his Munster contract. Life goes on.
"He is doing a lot of individual things," Erasmus continues.
"Of course there is definitely a lot more focus on small little things. We in the southern hemisphere and South Africa can spread the talent sometimes and don't really refine it.
"We are taking individuals one-on-one and helping them a lot. I think that's a culture we are trying to create and bring back into South Africa.
"If you look at the New Zealand game, they thoroughly deserved to beat us, but I still thought we created opportunities which we could have scored a few tries from.
"I think Felix had a lot to do with that. So he is not just focusing on the opposition structures, he is helping with our attack as well."
Erasmus' knowledge of the Irish system and northern hemisphere rugby will also prove to be invaluable.
With Thomas du Toit joining the squad this week, there are now five members of their set-up who were recently with Munster. Erasmus believes his time there opened his eyes to a different kind of rugby.
"People underestimate PRO14 rugby," he insists. "It is one of the toughest competitions I have coached in. It compares on all levels to Super Rugby because it is physical, tactical, it is different styles every week.
"So it is really a challenge where you have to do lots of analysis and that's where players I feel really have to grow and take ownership of the game and which eventually makes them better players. I am saying this with the utmost respect because I have been part of the South African system since 1994, sometimes you just play a lot on talent and we back that talent always.
"What we learned while working with Munster, and from Joe Schmidt and all the guys there, I respect Joe a lot from the few times I had contact with him. They only have 160 professional players but they manage those players like precision farming.
"They get the best out of the players and make sure that when they start with them, six months later they're really refined in all departments of the game. That would be a difference.
"Without a doubt. I became a better coach in Ireland."
Felix Jones will no doubt feel the same after working with South Africa.