Just a little something here that I just only noticed yesterday while I was making this gifset. But Luna is like wearing a nightgown there, which has a very symbolic meaning in my opinion. She is about to slumber , almost ready to rest. But she cannot not yet do that fully, as we know she continues on aiding Noctis even after her passing in some ways.
Darkness is taking her away and Noctis drifts off into the light. He lives, she dies. He walks in the light, she slumbers into darkness. Awaiting the light of the chosen one to pierce together with him through the darkness, to know eternal peace together at the end.
This is purely my interpretation, and works for me and makes it even stronger, their relationship I mean :D