The 24-year-old was among the Kiwi Ferns' best performers in their pre-tournament trial against the New Zealand Maori earlier this month, despite being in just her second full year of rugby league.
"There is a lot of pressure there because Sarina is pretty much the best fullback in New Zealand and I have looked up to her for so long. I used to watch her on TV, so it is pretty special for me to take over that role," Nicholls-Pualau told NRL.com.
"I just want to play how she does."
A convert from rugby sevens, where she played on the world circuit against fellow 2017 Kiwi Ferns teammate Honey Hireme, Nicholls-Pualau was originally set to play at the World Cup in a different coloured jersey, having trialled with her country of birth, the Cook Islands.
She will instead get the opportunity to come up against the nation in pool play, with New Zealand to meet the Cook Islands on November 19 at Southern Cross Group Stadium.
"I would have been eligible to play for the Cook Island and I got the call from them to join their squad, so I went over and had a few training [sessions] with them. But when I came back the communication between myself and the management wasn't good, so the Kiwi Ferns gave me an opportunity and I took it," Nicholls-Pualau said.
"It wasn't such a hard a decision, as soon as I went with New Zealand I knew that was my decision, and I am glad I stuck to it.
"I am looking forward to playing the Cook Islands, I pretty much know half of their team. I think I will be really confident in that game."
Corey Rosser | @CoreyRosser23
New Zealand Correspondent, NRL.com