The 25-year-old Western Force hooker is among the four uncapped hopefuls in McKenzie's preliminary 32-man squad, having stubbornly refused to let the debilitating genetic disease stall his inspirational rise to the top flight of a full contact sport demanding unflinching courage, skill and stamina.
Overcoming adversity is an oft-repeated cliché in professional sport, but Charles has lived with a far more sobering truism - that cystic fibrosis, a disorder that attacks the lungs and other major organs, means a death sentence for half of sufferers before their 40th birthday.
Charles explained how he overcame such adversity:
"My parents told me there was nothing in this world I can't do, and said 'if you want something, you go and work your arse off to get it' and that's what I did.
"That's the philosophy I've had all of my life and I've never let anything get in the way of achieving the goals that I want."
In a country where rugby writers speak of a game sliding gradually but inexorably toward financial oblivion, Charles has been a shining light for the embattled code, reminding fans of greater issues at stake than scorelines, bottom lines and win-loss ratios.
When diagnosed with CF as a baby, Charles's parents were told their son might not live to be 10 years old.
Seven years after his 10th birthday, the Sydney-born Charles was picked for the national Schoolboys rugby squad in 2006, having also excelled at rugby league and mulled pursuing a professional career in the rival code.
He notched his 50th cap with the Perth-based Force last month, an achievement all the more impressive after coming back from a serious knee injury that blighted his season last year.
It's hardly something he can ignore. A daily regime of dozens of pills and vitamins to keep fit and quell potentially lethal infections developing in his major organs is a constant reminder.
A build-up of mucus, caused by a gene disorder, means breathing difficulties.
Sufferers also face problems with their digestive system and struggle to put on weight:
"By the looks of me, obviously I don't have a problem with digestion. I eat plenty but mostly it affects me with the lungs.
"It creates an extra mucus for the lungs and clogs up the airways a bit, but fortunately I look after myself and keep myself in tip-top shape so it doesn't affect my on-field performance."
Beating the disease has meant embracing it, rather than ignoring it or pretending it doesn't exist.
That has meant being a national ambassador for Cystic Fibrosis Australia, the country's peak organisation fighting it, since 2010. His former Force coach Richard Graham said it was not always the case:
"Nathan ... initially, I think, kept (his CF) quiet because he was possibly a little bit embarrassed, didn't want people to think it would hold him back.
"But since he's come out and made us aware of it, I think the kid has blossomed."
The only CF sufferer playing top-flight rugby, Charles will battle long-serving hookers Stephen Moore and Tatafu Polota-Nau for spots in McKenzie's matchday 23s against Les Bleus in Brisbane, Melbourne and Sydney.
McKenzie insisted he was there on merit and merit alone:
"I think he's had a very good season, and he's a very consistent lineout thrower.
"Now the challenge for him is to step up and be influential at the next level."
Charles has been a driving force at a team enjoying its own fairytale this year.
Long Australia's plucky but underachieving team in the southern hemisphere competition, Force notched their eighth win of the season against the Johannesburg-based Lions on Saturday, a franchise record since joining the tournament in 2006.
Sitting fourth in the table with four rounds left in the regular season, Force have their hopes of a maiden play-off campaign firmly in their hands, but face a tough assignment against New Zealand's powerful Canterbury Crusaders side in Christchurch on Friday.
Victory, however, would be just one more surprise for a team - and player - that have confounded expectations.
- Sports & Recreation
- Nathan Charles
- cystic fibrosis
- Western Force