They became friends, and he found out Havas had made two films linked with the Maori Battalion in the 1970s. He watched them and thought other people would be interested.
Havas was on the island of Crete in the 1970s when he learned the story of Ned Nathan, a Maori Battalion soldier left behind on the island. He later married a Cretan woman and took her home to New Zealand. Havas made a film of the story, and Mr Nathan became a friend.
Then Mr Nathan asked him to film a 1977 trip by 500 people - veterans and their wives and families - to revisit places where the battalion fought in World War II. That film was called Sons of Tu Matauenga.
Last year Havas made the trip all over again, with Arahanga, for the Beyond the Battalion documentary. They finished up at Mr Nathan's Northland marae, where young Maori men in a leadership academy asked permission to use his name for their 2018 intake.
The 50-minute documentary includes pieces from both Havas' films, and new footage.
It took a bit of splicing together, Arahanga said.
Only six Maori Battalion veterans are left, and the film poses some interesting questions.
"We all have the fond memory of these guys, these heroes. The holistic story is a lot more complex than doing a haka and charging," Arahanga said.
In the next years the families of those veterans may talk about how tough it was to live with men who did the things people do in a war.
"There was no post-traumatic stress disorder therapy for those guys. What those men have carried inside is a lot of pain.
"Those are the kind of themes that we are interested in hearing and exploring. We need to talk about them, or they're always going to be unresolved," Arahanga said.
He will soon be looking for finance for three feature film ideas, and is also working on a new series called Reo Rangatira, about non-Maori who are fluent speakers of te reo Maori.
"It's about how Maori language and the Maori world view have affected their lives. We've got some really, really interesting subjects for that."
