So "Yda" is definitely the Girl in Red from the Stormblood trailer, buuuuuuuuuut it's still not #2Monks. None of the scions have job crystals, so it's actually Monk vs Pugilist /semantics!

Nero continues to be just the best. After their brief interaction in 3.56, I want Alisaie and Nero as traveling companions in 4.0 even more now. (Yugiri and Nero wouldn't be as good, but would still be fun.)

I'm pretty sure the spy mentioned in the stinger cutscene is just of the generic sort that we've seen all throughout the story. Every rank and file soldier in Eorzea knows that they're calling the new primal Shinryu because that's what the Doman's named it. There's no reason to assume it's someone close to us.