Black Ferns star Ruby Tui has opened up about a turbulent childhood and seeing a woman overdose and die while visiting a house with her father as a 10-year-old.

She also told TVNZ's Sunday of escaping to a women's refuge with her mum after enduring violence at the hands of one of her mum's partners.

Tui described self-harming at her lowest point, which she acknowledged would be hard for her family to hear.

"When I was 10 I thought I would never get out of this...I want kids to know it's not forever, you're not condemned, you can choose," the 30-year-old said.

"It was a pretty harrowing experience, watching someone OD like, basically in our arms. Dad and I were trying to save her, watching her body go limp with dad, and dad being really upset because he was trying to help her.

"It was a bit of a pivotal moment in my life, because drugs were so casual as a kid."

Her childhood wasn't perfect but she said she loved her parents, who would be cheering her on at the upcoming Rugby World Cup.

Tui said the tournament "would go down in history".

"I'm standing here, I'm a rugby player, I'm a female, I've got a brown face. I need to put this brown, female face up in here," she said.

"Women's rugby is such a huge vehicle for change and, you know, sticking up for things you should believe in. And I know if Aotearoa gets behind the Black Ferns, we're going to blow the world away. Like, we're just going to blow the world away."

Two weeks out from their maiden home World Cup, the Black Ferns made light work of world No 13 Japan on Saturday with Tui scoring a try as part of the 95-12 warm-up victory.

Despite being reigning champions and playing the tournament on home soil, the Black Ferns aren't going into the competition as the team to beat - the favourites are France and England, who dismantled New Zealand late last year in two Tests.