1484 /checkparam with this imperfect set on Mithra master NIN/WAR, no food/buffs:
ItemSet 361620
Adhemar+1: A path
Cape: DEX+30/Acc+20 augs
Could bump this up further to push it over 1500:
+11~12 Acc from Ninja Nodowa +2 with max augments (same 25acc as Moonlight, but max augment adds DEX+15... as well as Racc+25/AGI+15 for Daken)
+2~3 from cape (my JSE cape has DEX+30/Acc+20, could squeeze out a tiny bit more acc with DEX+20/Acc+30)
+10/+22 Acc from subjob /DNC or /RNG (though not likely a worthwhile cost)
+9 Acc to swap out Happo+1 for a Yamarang (though that's probably almost always a bad decision for NIN due to losing Daken TP generation).
1516 accuracy (+/- 1 acc depending on total DEX) assuming swaps to (i) JSE+2 neck (max augs), (ii) max acc cape, (iii) /DNC, and (iv) Yamarang
I may be missing some other minor increases. Also, some of this isn't exactly realistic in practice. For instance, would almost surely be worth the minor hit in accuracy to drop the AF+3 legs/Regal Ring combo in exchange for Kendatsuba+1 legs and another Ramuh Ring +1 (or Cacoethic+1, which is really a better call for NIN due to also adding Racc+16 for Daken).
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Edit: a more "realistic" goal super high acc set for NIN would be something like this, accounting for a better realistic mix of multi-attack, acc/racc (with NIN being a little weird in that Racc is important for TP too, thanks to Daken procs), tons of Meva (which tends to be useful on the stuff that would be demanding enough to require such high melee accuracy), etc.
ItemSet 361623
Acc: 1460
Racc: 1393 (1293 base plus inherent Daken Racc+100 bonus)
(Daken rate +79%: 40% trait/14% gifts/25% neck)