Of all the positional conundrums All Blacks coach Ian Foster will weigh before confronting Ireland in July, settling on a midfield combination is among his most scrutinised.
The loose forwards, where Blues captain Dalton Papalii is forging a compelling case to start alongside Ardie Savea and Sam Cane, will cause serious debate as Ethan Blackadder and Akira Ioane, who returns for his first match of the season this weekend, push for the blindside role.
So, too, are big decisions required in the front-row where swift evolution is needed, particularly in the wake of Joe Moody's season-ending knee injury.
New Zealand's midfield, though, contains a litany of juxtapositions Foster must unpack.
After a COVID-disrupted season that forced the All Blacks to carry an enlarged squad and heavily rotate, Foster is determined to embrace much more selection continuity as he attempts to settle on combinations before next year's World Cup. In the midfield, that first-choice combination remains uncertain.
Anton Lienert-Brown's six-month recovery from shoulder surgery robs Foster of his most experienced midfielder. With Lienert-Brown's calm head, his ability to slot in seamlessly at second five-eighth and centre, absent the door opens to others.
While he remains lethal from the left wing, where he's played 30 tests, Rieko Ioane started nine times for the All Blacks at centre last year and he continues to press his claims there with the Blues - last week claiming a vital intercept try against the Fijian Drua.
Ioane's strength and speed are expected to see him retain the starting centre role against Ireland but the 25-year-old can be exposed defensively when shooting out of the line in the Test arena. Last year Ioane and David Havili combined five times in the All Blacks midfield - the latter wearing the No. 12 jersey in nine Tests.
Early in the season Havili seized his chance against Fiji, the Wallabies and Pumas but, by the end of the year, the All Blacks lost faith as he struggled with the suffocating defensive pressure the Springboks, Ireland and France imposed.
Havili's natural skills are more suited to fullback, where he featured for much of his career before last year, but he made a decent fist of transitioning to second-five full time in 2021 and has continued in the role with the Crusaders this season.
Elevated for his international debut against Tonga, Chiefs second-five Quinn Tupaea gradually surpassed Havili to register his fifth start in the final Test of the year, the loss to France in Paris. Tupaea's direct, simplistic presence impressed and while he scored two tries from the left wing in a makeshift Chiefs backline last week, he remains in contention for the All Blacks midfield.
Jordie Barrett is the wildcard option - his temporary switch from fullback to second-five for the Hurricanes this season generating widespread debate about whether Foster would be swayed to do likewise.
The answer, at this point anyway, is don't count on it as Foster values Barrett's skills at fullback.
"Has it piqued my interest? I'm always interested in what teams are doing. Jordie and I have spoken about it," Foster said. "If it's the right thing for the team we understand that but it probably doesn't change our plans too much.
"He goal-kicked so well, his high-ball stuff is very good; he's got a strong kicking game and they were things he was able to exhibit through the year.
"Particularly when you get to the Northern Hemisphere style you have to have the ability to deal with that high ball and make sure you've got a strong kicking game in your back three. He ticked those boxes. He wasn't at his best against France but the rest of the tour I thought he was one of our success stories."
Jack Goodhue looms back into the equation after completing his comeback last week after a year out following knee surgery. While he missed last year's Test season, Goodhue immediately returns to the frame, with the ability to cover both midfield roles.
In the Crusaders' scrappy win against the Melbourne Rebels Goodhue played 52 minutes at second-five, running for 64 metres in six carries, beating four defenders and making one offload to evoke a glowing assessment from Crusaders coach Scott Robertson. "He was exceptional, his skill set," Robertson said. "I thought he was really tough with a lot of the carries, made some really good decisions on the field. So we're pleased for him that he could get such a positive start."
Robertson now faces a headache of how to shoehorn three All Blacks - Goodhue, Havili, Braydon Ennor - into his midfield. That's before you consider Leicester Fainga'anuku, who has been knocking down the All Blacks door from wing and centre for the past two seasons.
Question marks remain over Fainga'anuku's best position, particularly his defence and distribution from centre, but his power and dynamic running lines are impossible to ignore.
Other fringe prospects, including Chiefs and Māori All Blacks midfielder Alex Nankivell and Highlanders centre Thomas Umaga-Jensen, the latter a consistent performer in a losing team this season, must also be in the conversation.
Ultimately, the All Blacks need to determine the traits they desire from their second-five. This is the position they have not filled since Ma'a Nonu's departure after largely shunning Ngani Laumape prior to his departure to France.
Last year's experiment with asking Havili to shoulder some of the playmaking responsibility started promisingly, only to stall in the face of world-class defensive systems.
The best midfield combinations are complementary. Power and punch. Deception and distribution. Guile and grunt. The All Blacks are yet to find their ideal, balanced duo.
Of the plethora of contenders available to Foster he appears destined to land on Goodhue and Ioane combining for Ireland, with Tupaea and Havili possibly contesting a bench spot.
Eighteen months out from the World Cup, time is running out to settle on the preferred midfield mix.