Neighbours heard Oti swearing, thumping noises and a person crying out in pain.
Judge Matthew Muir said he slammed his cousin's head into the floor multiple times "with considerable force" around 5.30am, and earlier stomped on his chest, fracturing his ribs.
This final beating - which lasted 30 to 40 minutes - is what ultimately led to his death, Justice Muir concluded.
Oti, 47, went to sleep and found him "motionless and cold" on the bedroom floor around noon the next day.
He initially lied to police about his involvement.
Oti was found guilty of murder by a jury trial which ended on May 7.
Today the victim's brother, Oti's cousin, said he treats Oti like a brother despite the death.
He looked Oti in the eye as he read his victim impact statement at the High Court in Auckland.
"Was he an idiot? Yes he was," he said.
"Tainui you're still a brother to me. My whānau forgives you.
"There is no excuse for what you've done.
"If they throw everything at you, you deserve it. But we are whānau. I love you."
Oti went to shake his cousin's hand before security guards pulled him away.
The pair had participated in restorative justice hui.
Oti is committed to the process of change, Niven said, and has shown remorse.
The court heard how Oti had abused alcohol and drugs.
Oti's family based in Queensland sat through the sentencing via audio visual link.
Where to get help:
• If it's an emergency and you feel that you or someone else is at risk, call 111.
• If you've ever experienced sexual assault or abuse and need to talk to someone call the confidential crisis helpline
Safe to Talk
on: 0800 044 334 or text 4334.
• Alternatively contact your local police station
• If you have been abused, remember it's not your fault.