He lost control and flipped the car on Shakespeare Rd, near Napier CBD, after speeding away from police who had abandoned a pursuit, the court heard.
His cousin Harmony Te Pou, 20, was in the boot and died at the scene.
The court heard he was estimated to have reached speeds up to 120km/h in a 50km/h zone through Napier CBD, as his passengers shouted at him to slow down.
He was sentenced to five years and eight months imprisonment at the High Court in Napier on Friday.
There was no non-parole period set, which means he will be released from jail in 2029, considering time already served.
He pleaded guilty earlier this year to manslaughter, seven counts of reckless driving causing injury and one count of failing to stop.
Several powerful victim impact statements were read out as part of the sentencing and a large family gathering was present at the back of the courtroom.
“In some ways, the reading of these victim impact statements to Mithias today is his sentence,” Justice Matthew Palmer said at Friday’s sentencing.
Mithias, who has a distinctive facial tattoo, sat between two Corrections staff as the statements were read and the sentence was handed down.
His then-partner suffered awful injuries in the crash and is now paralysed from the waist down. The pair have three children together.
Harmony’s partner suffered a brain injury and cracked skull during the crash, among other injuries, and still suffers from memory loss.
Harmony’s mother, Kuini Te Pou, told the court her daughter was “the light in our family” and “was able to make us all smile even if we were having a bad day”.
“Harmony is present in every single one of us but her light is not with us any more and that cuts deep.”
Kuini said one of the last things Harmony said that night was addressed to her yet-to-be-born nephew. She was set to be the baby’s godmother.
“She touched and kissed the belly of [her brother’s partner] and said, ‘I can’t wait to meet you my boy’ – and then she was gone.”
Kuini said her daughter had previously lost two close friends in another fatal car crash.
Mithias’ upbringing was taken into account, including his first being offered meth by a relative at the age of 11 and being taken into state care at 13.
His remorse, his drug problem combined with undiagnosed mental health issues and his early guilty plea were all considered in setting the jail term.
Gary Hamilton-Irvine is a Hawke’s Bay-based reporter who covers a range of news topics including business, councils, breaking news and cyclone recovery. He formerly worked at News Corp Australia.