Gaia's Outfit on Mogstation

[Arrius]

There's videos on YouTube to explain the process of porting and fitting clothes to new models if you want to literally see it.

In a nutshell though, they basically exported the garment, removed all of the parts of the jacket and (I don't know specifically what mod it is so I can only guess from here) upscaled it to a different/multiple modded bodies or refit the edited garment back to the vanilla bodies.

As far as the splitting, I'm moreso willing to guess that the outfit was originally in separate pieces (as was the case with Lyse's gown) and Square was the one who fused them into one. I can't say for sure unless someone can get a hold of Gaia's model in Eden wearing the dress and check that via a certain gpose program.

Likely it's rigged for Gaia only and when you wear that outfit you basically perform a bodyswap to match her body.