With barefeet, basic shorts and a T-shirt, Mr Souza sat on the slackline and bounced three times, giving himself enough momentum to spring up on to his feet. Waving his hands above his head to counteract movement, he placed one foot after the other before bouncing again, in a measured series of movements, to perform leaps along the bouncy line.
Then he paused, crouched down on the line and balanced, with his legs in a diamond shape and his hands poised together in prayer position.
Similar to the circus act of tight-rope walking, slacklining dates back to the 1980s where it was first used by rock-climbers.
It has since exploded around the world and developed into a sport that Mr Souza said now sparked fierce competition.
The Brazilian said he turned to slacklining to improve his balance, concentration and overall mindset to carry into his day-to-day life.
"I was looking for a sport with a relationship between trees and nature.
"It is very popular in Brazil but I was the first person to do it where I am from."
Peter Rowe, owner of Auckland store Gibbon Slackline, said he understood slacklining had been in New Zealand for about 10 years and although it was still small it was "definitely getting bigger".
"I first tried it when my kids started doing it. It's a great outdoor activity. Kids usually outgrow sports but this one you can do forever."
Although anyone could try slacklining, Mr Rowe said he advised people to always start with the line just off the ground until they became confident.
He said the more dangerous version - highlining - usually always had safety features such as a harness or a secondary line.
It was more popular in the bigger New Zealand cities and some Auckland schools even offered it, he said.
"Parents of teenage kids, to get them outside playing, this is great for that," Mr Rowe said. "It's great for the core, the mind, the balance."
There was now a Facebook group for New Zealand slackliners and they organised "meets" regularly throughout the year.
Mr Souza travelled to Napier to improve his English.
"I like the size, the people [are] nice, and good places for slacklining."
He is known to slack-off often, and can sometimes be spotted among the treetops, in solitude, poised on a line some metres above the ground.
