The court heard that four men arrived after Wirihana had an altercation with his partner's aunty and a chaotic fight broke out. Wirihana was bashed and hit on the head with a shovel. Amidst the melee, a vehicle was driven towards Wirihana and reversed, pinning his partner's leg against another vehicle, before it crashed into the house.
Wirihana grabbed a knife from inside the house and lunged at Mason through the passenger window, fatally stabbing him in the neck.
In December 2021, a jury found Wirihana not guilty of murder, but guilty of manslaughter. Wirihana was acquitted on two counts of disfiguring with intent to cause grievous bodily harm.
Yesterday, Wirihana's lawyer Adam Holland told the court there was "clearly a profound imminent threat and provocation when Mr Wirihana made the decision to jump into the car with a knife".
"Not only was he trying to defend himself, he was trying to defend his partner."
Holland called for a starting sentence of four years, citing Wirihana's remorse and early plea, but the Crown argued for a starting point of seven to nine years.
Justice Rebecca Edwards accepted starting at seven years but reduced this by 25 per cent for Wirihana's early guilty plea efforts. Judge Edwards gave a further 10 per cent discount for Wirihana's remorse and another 10 per cent for mitigating factors such as PTSD and past head trauma.
Justice Edwards told Wirihana: "That does not excuse what you did or absolve you of your responsibilities but it does help to explain."
Justice Edwards acknowledged the family and friends of Wirihana and Mason who filled the public gallery, saying the day would be "a difficult day for you all".
"[The sentence] is not a measure of a victim's life. Nothing I say will undo the tragic events that led to Mr Mason's passing."
Justice Edwards told the court Wirihana was set upon and outnumbered, and it was clear that his attackers were hyped up and aggressive, intent on doing harm.
"I accept that there was provocation in the events leading up to the stabbing. However, by the time you came to stabbing Mr Mason, the car had come to a standstill, having crashed into the house. The imminence of that threat had subsided. You could have moved away.
"You told police you were feeling rage at this point as a result of the attack."
This was Wirihana's second serious court appearance, and under New Zealand's Three Strikes legislation, due for repeal in July, he must be ordered to a sentence without parole.
However, Justice Edwards declined to impose this because she said to do so could be a breach of the Human Rights Act by imposing a more detrimental impact on Wirihana, she said.
"It would crush that spark of hope that is so integral to rehabilitation," Justice Edwards said.
"I consider there to be a real risk . . . which will simply compound the impact of social deprivation and further I consider that to be an unjust and inappropriate response."
Justice Edwards said she had not overlooked the views of Mason's family, saying no loved one should have to go through the experience they did and the impact on his wife and daughter was "immense".
"It's clear that Mr Mason was much loved in his whanau."
Wirihana could be eligible for parole after a third of his sentence is served.
