The teams were named yesterday and Nareki has been selected, but Vilimoni Koroi has not been picked, as rest is the preferred option for the promising youngster.
Koroi has had a very busy year with sevens commitments, along with starring for the New Zealand under-20 side.
A plan hatched last year by New Zealand Rugby bosses decided Koroi would not be available for the World Cup, as his workload had to be managed. With sevens and playing for Otago, there is a danger Koroi could play the whole year round.
Nareki signed for the sevens squad last year but did not make his first tournament appearance until Hong Kong in April and impressed enough to play in the London and Paris tournaments.
Both teams travel to the United States this weekend as defending World Cup champions. A high-stakes new knock-out format effectively equalises the playing field for the 24 countries in the men's tournament, and 16 national unions in the women's field.
All Blacks Sevens coach Clark Laidlaw said the unique nature of the knock-out competition contributed to it being a difficult squad to select.
''Getting the balance of the squad right was the main thing. It's a different tournament in that it's four games instead of six and we can only take 12 players, so we were looking to have flexibility in the 12 in terms of the positions they cover,'' he said.
''No team has ever won back-to-back World Cup titles since it's started so we have certainly talked about that and about being the first team to change that. We know there are massive challenges to come; all the teams will be really well prepared.''
Black Ferns Sevens coach Allan Bunting said this was the most challenging squad he had ever had to name.
''It was definitely hard but that's exactly where we want to be. In our trials there was so much motivation, excitement and skill set - we know we have selected the right team,'' he said.