The pair are second cousins and share a supportive bond that would be rare for any players battling for the same position in Test rugby.
Both are likely to be in the 23 for Saturday’s pool opener at Sapporo.
Fainga’a insists he won’t be put out if his older relative wins the No.2 jersey, as he is favoured to do.
“Starting, not starting, on the bench, whoever’s got that jersey on, it’s just do your best for the team,” he told journalists at the Wallabies training base in Odawara.
“There’s no ‘if I see you, I’m going to smash you’. It’s just to get the team ready for the weekend and to keep each other accountable and push each other to be better.”
Latu’s mother and Fainga’a’s father are cousins and watched on when their children played together at junior level in Sydney.
Even though Fainga’a has moved to Canberra, the wider families remain close and are never short on advice.
“Everyone’s overwhelmed. To get to do it next to my own blood cousin is pretty exciting. We’re into each other at training all the time, giving each other s..t, just to drive each us to be better.
“His mum and his family, we always get told not to be with each other because we always get up to no good.”
It is the first World Cup for both hookers, who are favoured to be selected over a third tournament rookie, Jordan Uelese.
Latu was an earlier developer, already into his second season at the Waratahs when the last World Cup was played.
Fainga’a was at a crossroads in 2015, having finished with the Australia junior team as a back rower and taken up some labouring jobs because of uncertainty over his rugby future.
That changed when he joined the Brumbies and shifted to hooker.
He was star for the Australian Conference winners this year, scoring 12 tries, mostly from lineout drives.
It was a contrast for Latu, who made sporadic Super Rugby appearances in 2019 because of two suspensions – the second following a drink driving charge.
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