Hm. So some things I’m kinda been pondering about. First what happened to those from the City at the end of 3? They’re technically not a part of Keves or Agnus so when the worlds split were they retcon’d out of existence?
The City's inhabitants are technically a mish-mash of Kevesi and Agnian inhabitants, forming a society away from Moebius (hence the eyepatch and the Alloy within). Grey, for example, is ex-Kevesi, but the twist is that he's a member of the Lost Numbers. Ghondor and Monica, on the other hand (and idk if this carries into story, I'll have to double-check), are interpreted as Agnian for Gameplay purposes. It's likely that Swordmarch's inhabitants would stay on the Kevesi side, knowing that it's the Mechonis sword, which logically should be Kevesi (XC1/Melia) property.
Another thing I’ve been pondering is how Nia became Queen? I could understand Melia being one since she’s High Entia royalty and after the world of 1 being remade the people would probably have her be their ruler. But Nia? If 3 is supposed to be like some decades after 1 and 2 instead of centuries, then how did she end up becoming ruler of their world when surely the leaders of the other nations would still be alive like Nial?
My guess is that Queen Raqura stepped down at some point, and knowing that Uraya was butting heads with Mor Ardain (Because Mor Ardain was trying to annex Torigoth for the longest time), Nia likely landed herself a job there (recognition for saving Alrest from Malos and all that). Still, an explanation probably resides within the DLC.
Finally, not really a question but something I took note. It’s interesting how everyone in 3 can summon their weapons like Blades did in 2. I could understand people from Agnus doing so since everyone there is probably a Blade hybrid. But apparently those from Keves can do so as well. Perhaps the Power Disks they wear does that for them? Of course I know it’s a gameplay feature but just something I pondered about.
I have to agree here, the Staff Melia was using in FC doesn't behave like it does in XC3. Then again, it's not impossible knowing that Alcamoth in XC3 effectively had a post-Mechonis makeover.