What about a crossover with "Stranger of Paradise"?

[Cilia]

There was already a crossover in Stranger of Paradise. One of the first areas of the game is quite literally Sastasha.

Pravoka Seagrot is Sastasha with the serial numbers filed off...

... but we haven't gotten anything from SoP in this game. Not sure what they'd use though, given the two games are tonally inconsistent and the SoP characters don't exactly have distinctive outfits or hairstyles. Something like Tyrant would be a pretty cool Job here, but given XIV has all but abandoned elemental affinities as relevant I'm not sure how that'd work.