But the 29-year-old Carfrae is the first reigning champ and arrives full of confidence as the favourite.
"Winning Kona was a huge goal for me," said Carfrae. "To tick that off in just my second time in Hawaii was great. It has set me apart from many others - in that I have that world title.
"But I don't really see myself any differently. I love the sport and I love racing - and want to keep improving.
Carfrae has set a new women's record for the run at Kona both times she has competed in Hawaii. She says her rapid rise to the top of ironman, arguably one of the world's most physically demanding sports, has surprised even her.
But seven-time champion Jo Lawn is hoping to teach Carfrae a lesson. The 37-year-old Kiwi is gunning for title No8 and is ready to race after a run of good results.
Last month Lawn won the Port of Tauranga Half, taking 5min off the time she set at the event in 2009.
"I felt fantastic throughout the whole race and it is great to have the title of New Zealand's long-distance champion," said Lawn, who will defend her ironman title on Saturday.
Getting her head around a tough training load is compatriot Samantha Warriner, who confirmed her entry only 14 weeks after heart surgery.
Warriner put plans to renovate her kitchen on hold to pay for the $25,000 operation in December for super ventricular tachycardia, or a racing heart beat.
"I had been told as a child that my heart was too big and that it would go into spasm now and again (racing to 230 beats per minute).
"I really did not think much about that, and the odd time that it must have gone off I felt some discomfort and I just stopped (exercising) and it settled."
When she hit the operating theatre, Warriner was more nervous than she expected. But the procedure was completed without any problems and week later Warriner was back training, and formed a game plan for her first ironman with new coach Jon Ackland.
"Gradually, under Jon's strict control, I have got back into things," she said. "We decided that a great project would be to take on my first Ironman, and where better to do that than at Taupo?"
Warriner, a former roommate of Carfrae, has the long-term ambition of making it to Kona this year. If she does, it would be another chapter in what is already a great comeback story.
Peter Thornton