Phoenix has a strict regime of creams and moisturisers, and is almost entirely wrapped in bandages when his condition is at its worst, but it's the emotional effects that worry his mother, Janie Witehira (Waipapa).
"He notices when adults pull their kids away or when other children stare. He started to cover his face in social situations. He didn't care about the sores, it was people staring at him," she said.
Mrs Tupara said Phoenix was about two years old when he started noticing superheroes. When he wore a Spiderman costume his facial bandages became part of his superhero identity, something to wear with pride rather than shame.
And when he saw Flat Man on a TV earthquake report he felt an instant bond.
"He said, 'He's a superhero, and he looks just like me.' It made him proud of who he is, and he started telling everyone who would listen that his name was Flat Man."
When one of Phoenix's home tutors contacted Flat Man to tell him about his young fan, that was all the prompting the southern superhero needed. He launched a fundraising drive, and soon had enough money to treat Phoenix and his grandmother to a superhero's day out.
On March 25 they were flown to Christchurch on an all-expenses-paid trip with a welcome at every airport and on every plane. When they landed a crowd of superheroes was waiting with gifts and banners.
"Then the tears really flowed, I felt the love of those people," Mrs Tupara said. She responded the best way she could, with a karanga that rang out through the arrivals hall.
They were overwhelmed by their hotel, a place fit for "kings and queens," and were showered with yet more gifts, including a signed Crusaders jersey. They were treated to a morning tea hosted by Mayor Lianne Dalziel, a tour of the Antarctic Centre and a ride on the Christchurch Gondola.
Flat Man and Phoenix spent hours at Hagley Park playground, where even feeding the ducks was a new experience for Flat Man's mini-me. Coverage in local media meant the young superhero was recognised and greeted everywhere he went.
For Mrs Tupara the trip was made even more emotional by seeing first-hand the earthquakes' devastation.
"What really took my heart was that they've lost so much, but they can still reach out to a little boy in the Far North. That takes a very special community," she said.
And now Flat Man was now planning a trip to the Far North to see Phoenix again. He had only visited a marae as a schoolboy, so a welcome at the family marae at Mataraua was top of his itinerary.
Meanwhile Flat Man was equally moved by meeting Phoenix and the "incredible woman" he now calls Wonder Gran, describing it as a "a very emotional, heartwarming experience". "Anyone who embraces their inner superhero deserves to have a special day, and for Phoenix to go through what he has and still be so full of confidence, love and kindness is amazing," he said.
"Their visit was far more emotional than I'd planned, and it has changed me for the better. I dream to be able to create super days like this for more children. We've definitely created a super bond that we'll always have."