It has been a challenging season for the Chiefs midfield. Aki has been one of the positives, along with the way Nanai-Williams has converted to centre, but now that he has been ruled out with a groin problem, for which he will need surgery, much of the onus will fall on 23-year-old Aki, who is playing his first season at this level.
Coaches Dave Rennie and Co have selected seven different midfield combinations. The absence of Sonny Bill Williams has been keenly felt, as they knew it would be, but they have managed to find the consistency necessary to finish at the top of the table despite some bad luck.
Former All Black Richard Kahui was ruled out earlier in the season with yet another shoulder injury, leaving the Chiefs with one of the smallest midfields in the competition.
But as the players around him have come and gone, Aki has been a virtual constant at second-five - he has started 12 of the Chiefs' 16 matches in the No12 jersey.
Last year he was a member of the Chiefs wider training squad, a sideline to his main job as a bank teller for Westpac in Mangere. Now the Counties player is earning interest on a growing reputation.
"It's pretty unlucky for him," he said of Nanai-Williams' injury, "but I back the other players to step up and do what he's been doing. All the players that we have can do the same things he does.
"It's a good thing for the team," Aki said of the midfield rotation earlier in the season. "Everyone's on edge and with the injuries that we've had, the coaches have confidence in every player we have."
Now is a good time to have confidence. The Crusaders have not only shown an improvement up front, playmaker Dan Carter has hit a rich vein of form which is allowing the relatively new midfield combination of Tom Taylor and Ryan Crotty to flourish. Both Taylor and Crotty are smart, precise players. They are solid defenders too but perhaps lack the flair that Aki possesses.
Charlie Ngatai is likely to be Aki's midfield partner at Waikato Stadium. He and Aki played in both the Chiefs' matches against the Crusaders this season and Ngatai adds a bit of size to the No13 jersey which has been swapped around a fair bit.
Nanai-Williams has seen the most action there but Kahui, Ngatai, and Save Tokula have all played at centre.
Andrew Horrell, who has had ankle problems, has also been tried at second-five.
Aki, who scored the Chiefs' first try against the Blues in front of his family and former workmates at Eden Park, admitted he had been surprised by his progress.
"I actually have been surprised at how I've adapted in my first season of Super Rugby. I'm enjoying it at the moment and hopefully there's a lot to learn and hopefully I'll get better."
Counties coach Tana Umaga, the former All Blacks midfielder, has been a major influence, but Aki said all of the Chiefs coaches had had input into his progress this year - not only Rennie and Wayne Smith but also Tom Coventry and Andrew Strawbridge.
"They're a high-quality coaching staff and everything they've been teaching me has been helping."
It is the direction the former bank teller will be counting on in the biggest match of his career.
